Traffic_ Why We Drive The Way We Do Part 12

"fifteen-second rule": See, for example, Paul Green, "The 15-Second Rule for Driver Information Systems," ITS America Ninth Annual Meeting Conference Proceedings ITS America Ninth Annual Meeting Conference Proceedings (Washington, D.C.: Intelligent Transportation Society of America, 1999). (Washington, D.C.: Intelligent Transportation Society of America, 1999).

"and they're in trouble": This raises the interesting question of why people who were following closer closer than two seconds did not account for the majority of rear-end crashes, as one might suspect. Klauer suggested that when people "are aggressively tailgating, or trying to maintain their position against all vehicles in their surrounding environment, they're paying very close attention." Does that mean we should all tailgate? "It's an interesting finding," Klauer said. "We tried to be very careful in the way that we reported that, because that's exactly what we did not want people to take away from this-'Oh, tailgating is a perfectly safe thing to do.' All we're saying is we didn't see a whole lot of crashes that were a result of it." This raises the question of which demon you would rather face: the driver hanging far back but talking on a cell phone or the frenetically attentive tailgater. than two seconds did not account for the majority of rear-end crashes, as one might suspect. Klauer suggested that when people "are aggressively tailgating, or trying to maintain their position against all vehicles in their surrounding environment, they're paying very close attention." Does that mean we should all tailgate? "It's an interesting finding," Klauer said. "We tried to be very careful in the way that we reported that, because that's exactly what we did not want people to take away from this-'Oh, tailgating is a perfectly safe thing to do.' All we're saying is we didn't see a whole lot of crashes that were a result of it." This raises the question of which demon you would rather face: the driver hanging far back but talking on a cell phone or the frenetically attentive tailgater.

like changing lanes: A simulator study by William Horrey and Daniel Simons found that drivers under "single" and "dual" task conditions did not change the s.p.a.cing they allowed during lane changing, unlike the greater headway drivers tend to allow when following a car and talking on a cell phone. The authors suggest that "dual-task interference might be more dangerous when drivers must actively decide how to interact with traffic than when their decisions are constrained by the driving context." W. J. Horrey and D. J. Simons, "Examining Cognitive Interference and Adaptive Safety Behaviors in Tactical Vehicle Control," Ergonomics, Ergonomics, vol. 50, no. 8 (August 2007), pp. 134050. vol. 50, no. 8 (August 2007), pp. 134050.

to their speed: See James Reason, Human Error Human Error (Cambridge: Cambridge Univeristy Press, 1990), p. 81. (Cambridge: Cambridge Univeristy Press, 1990), p. 81.

task got harder: J. Verghese, G. Kuslansky, R. Holtzer, M. Katz, X. Xue, H. Buschke, and M. Pahor, "Walking While Talking: Effect of Task Prioritization in the Elderly," Archives of Physical Medicine and Rehabilitation, Archives of Physical Medicine and Rehabilitation, vol. 88, no. 1 (2006), pp. 5053. vol. 88, no. 1 (2006), pp. 5053.

"sample the environment": A. Oulasvirta, S. Tamminen, V. Roto, and J. Kuorelahti, "Interaction in 4-Second Bursts: The Fragmented Nature of Attentional Resources in Mobile HCI," Proceedings of CHI 2005 Proceedings of CHI 2005 (New York: ACM Press, 2005), pp. 91928. See also V. Lantz, J. Marila, T. Nyyssonen, and H. Summala, "Mobile Measurements of Mobile Users," in Lucas Noldus and Fabrizio Grieco, (New York: ACM Press, 2005), pp. 91928. See also V. Lantz, J. Marila, T. Nyyssonen, and H. Summala, "Mobile Measurements of Mobile Users," in Lucas Noldus and Fabrizio Grieco, Proceedings of Measuring Behavior 2005: Fifth International Conference on Methods and Techniques in Behavioral Research, Proceedings of Measuring Behavior 2005: Fifth International Conference on Methods and Techniques in Behavioral Research, ed. (Wageningen, Netherlands, 2005). ed. (Wageningen, Netherlands, 2005).

longer to do so: J. Hatfield and S. Murphy, "The Effects of Mobile Phone Use on Pedestrian Crossing Behaviour at Signalised and Unsignalised Intersections," Accident a.n.a.lysis & Prevention, Accident a.n.a.lysis & Prevention, vol. 39, no. 1 (2006), pp. 197205. vol. 39, no. 1 (2006), pp. 197205.

suffers from a bottleneck: Mei-Ching Lien, Eric Ruthruff, and James C Johnston, "Attentional Limitations in Doing Two Tasks at Once: The Search for Exceptions," Current Directions in Psychological Science, Current Directions in Psychological Science, vol. 15, no. 2 (2006), pp. 8993. vol. 15, no. 2 (2006), pp. 8993.

forgot most of them: For a good summary of this research, see David Shinar, Psychology on the Road: The Human Factor in Traffic Safety Psychology on the Road: The Human Factor in Traffic Safety (New York: Wiley, 1978), p. 27. (New York: Wiley, 1978), p. 27.

is not useful to our lives: Indeed, scientists have demonstrated, neurologically, how forgetting things helps us in the process of remembering. See Brice A. Kuhl, Nicole M. Dudukovic, Itamar Kahn, and Anthony D. Wagner, "Decreased Demands on Cognitive Control Reveal the Neural Processing Benefits of Forgetting," Nature Neuroscience, Nature Neuroscience, vol. 10 (2007), pp. 90814. vol. 10 (2007), pp. 90814.

again for "confirmation": See Helmut T. Zwahlen and Thomas Schnell, "Driver Eye Scan Behavior When Reading Symbolic Warning Signs," in Vision in Vehicles VI, Vision in Vehicles VI, ed. A. Gale, I. D. Brown, C. M. Haslegrave, and S. P. Taylor (Amsterdam: Elsevier Science, 1998), p. 3. ed. A. Gale, I. D. Brown, C. M. Haslegrave, and S. P. Taylor (Amsterdam: Elsevier Science, 1998), p. 3.

("effectively blind"): See Graham Hole's concise and authorative study, The Psychology of Driving The Psychology of Driving (Mahwah, New Jersey: Lawrence Erlbaum a.s.sociations, 2007), p. 60. (Mahwah, New Jersey: Lawrence Erlbaum a.s.sociations, 2007), p. 60.

had already been made: H. Shinoda, M. Hayhoe, and A. Shrivastava, "What Controls Attention in Natural Environments?" Vision Research, Vision Research, vol. 41 (2001), pp. 353546. vol. 41 (2001), pp. 353546.

basketball players: Daniel J. Simons and Christopher F. Chabris, "Gorillas in Our Midst: Sustained Inattentional Blindness for Dynamic Events," Perception, Perception, vol. 28 (1999), pp. 105974. vol. 28 (1999), pp. 105974.

locked on the video screen: One of Simon's key findings is that subjects were less likely to see the gorilla when they were asked to count the number of pa.s.ses made by the team wearing white T-shirts. This meant, according to Simons, that people did not see the gorilla because it did not look like what they were looking for-or because it did did look like what they were ignoring (the team wearing black shirts). As Simons put it, "The more you're focused on what you expect to see, the less likely you are to see unexpected stuff." look like what they were ignoring (the team wearing black shirts). As Simons put it, "The more you're focused on what you expect to see, the less likely you are to see unexpected stuff."

"failure to see": The role that a car driver's vision (or lack thereof) plays in car-motorcycle crashes is huge: For nine of the ten types of leading car-motorcycle crashes, the motorcycle is proceeding in a straight line (with the most common being the car turning left across the path of an approaching motorcycle). See P. A. Hanc.o.c.k, G. Wulf, D. R. Thom, and P. Fa.s.snacht, "Contrasting Driver Behavior During Turns and Straight Driving," paper presented at the 33rd Annual Meeting of the Human Factors Society, Denver, Colorado, October 1989.

on the road: Another response, of course, is the "loud pipes save lives" approach, by which motorcyclists insist that an ear-shattering exhaust system will surely alert drivers of their presence. The problem is that drivers are often unaware of the direction direction of such sounds. Another problem is that for the people who have to listen to the loud pipes, the issue of saving motorcyclists' lives might not exactly be a pressing agenda. of such sounds. Another problem is that for the people who have to listen to the loud pipes, the issue of saving motorcyclists' lives might not exactly be a pressing agenda.

change lanes or slow down: USA Today, USA Today, July 4, 2007. July 4, 2007.

moths to a flame: At a meeting I attended in Los Angeles, for example, the California Highway patrol was concerned with a recent spate of these crashes, which had claimed the lives of six officers over just a few months. "For whatever reason they tend to find us on the side of the road," a CHP officer said at a traffic reporters' meeting one morning. "It's just a dangerous place to be."

we see something interesting: Driving simulator studies have suggested that drivers have a tendency to at least momentarily steer in the direction of their gaze, "in many cases without the conscious awareness of doing so at all." W. O. Readinger, A. Chatziastros, D. W. Cunningham, H. H. Bulthoff, and J. E. Cutting, "Gaze-Eccentricity Effects on Road Position and Steering," Journal of Experimental Psychology: Applied, Journal of Experimental Psychology: Applied, vol. 8, no. 4 (Dec. 2002), pp. 24758. In an e-mail correspondence, James Cutting made the further point that he thought the reason drivers were not constantly driving off the road when they looked at something had to do with balance: "The 'looking where you are going' phenomenon is, I think, strongly related to balance. This is why it is a problem with novice motorcycle drivers, and can have a small effect in walking. Balance is not much an issue in driving (although people do tilt their heads when going into a turn, and they obviously don't need to). Usually, when driving, one maintains direction while shifting gaze simply because the arm motions to make a turn are not reflexively relative to gaze direction. Balance is." vol. 8, no. 4 (Dec. 2002), pp. 24758. In an e-mail correspondence, James Cutting made the further point that he thought the reason drivers were not constantly driving off the road when they looked at something had to do with balance: "The 'looking where you are going' phenomenon is, I think, strongly related to balance. This is why it is a problem with novice motorcycle drivers, and can have a small effect in walking. Balance is not much an issue in driving (although people do tilt their heads when going into a turn, and they obviously don't need to). Usually, when driving, one maintains direction while shifting gaze simply because the arm motions to make a turn are not reflexively relative to gaze direction. Balance is."

their position in the lane: For a concise roundup of moth effect research, see Marc Green, "Is the Moth Effect Real?" Accessed from http://www.visualexpert.com/Resources/motheffect.htm.

while we are moving: See Mark Nawrot, Benita Nordenstrom, and Amy Olson, "Disruption of Eye Movements by Ethanol Intoxication Affects Perception of Depth from Motion Parallax," Psychological Science, Psychological Science, vol. 15, no. 12 (2004), pp. 85865. vol. 15, no. 12 (2004), pp. 85865.

for both cars: Martin Langham, Graham Hole, Jacqueline Edwards, and Colin O'Neil, "An a.n.a.lysis of 'Looked but Failed to See' Accidents Involving Parked Police Vehicles," Ergonomics, Ergonomics, vol. 45, no. 3 (2002), pp. 16785. Another study found that police cars equipped with the more visible roof-top bar lights were struck just as often as cars with the less visible rear-deck lights, also suggesting that visibility per se may not be the most important factor in these crashes. See Lieutenant James D. Wells Jr., "Patrol-Car Crashes: Rear-End Collision Study-1999," Florida Highway Patrol, 1999. vol. 45, no. 3 (2002), pp. 16785. Another study found that police cars equipped with the more visible roof-top bar lights were struck just as often as cars with the less visible rear-deck lights, also suggesting that visibility per se may not be the most important factor in these crashes. See Lieutenant James D. Wells Jr., "Patrol-Car Crashes: Rear-End Collision Study-1999," Florida Highway Patrol, 1999.

typically takes longer: Interestingly, a French study had subjects first take a Stroop test and then partic.i.p.ate in a driving test on a closed course that required an unexpected evasive maneuver. Subjects who did poorly on the Stroop test tended to also do less well during the driving exercise. Christian Collet, Claire Pet.i.t, Alain Priez, and Andre Dittmar, "Stroop Color-Word Test, Arousal, Electrodermal Activity and Performance in a Critical Driving Situation," Biological Psychology, Biological Psychology, vol. 69 (2005), pp. 195203. vol. 69 (2005), pp. 195203.

in the way of the less automatic: See Colin M. McLeod, "Half a Century of Research on the Stroop Effect: An Integrative Review," Psychological Bulletin, Psychological Bulletin, vol. 109, no. 2 (1991), pp. 163201. vol. 109, no. 2 (1991), pp. 163201.

(i.e., the word itself): This idea comes from Jennifer J. Freyd, Susan R. Martorello, Jessica S. Alvardo, Amy E. Hayes, and Jill C. Christman, "Cognitive Environments and Dissociative Tendencies: Performance on the Standard Stroop Task for High Versus Low Dissociators," Applied Cognitive Psychology, Applied Cognitive Psychology, vol. 12 (1998), pp. 91103. vol. 12 (1998), pp. 91103.

than the arrow: S. B Most and R. S. Astur, "Feature-Based Attentional Set as a Cause of Traffic Accidents," Visual Cognition, Visual Cognition, vol. 15 (2007), pp. 12532. vol. 15 (2007), pp. 12532.

consultant in California: P. L. Jacobsen, "Safety in Numbers: More Walkers and Bicyclists, Safer Walking and Bicycling," Injury Prevention, Injury Prevention, vol. 9 (2003), pp. 20509. The "safety in numbers" effect has been found in many other studies as well. For example, Noah Radford and David Ragland of the University of California at Berkeley looked at the city of Oakland, California. They found that nearly all of the city's most dangerous intersections were on the city's east side, an area with low pedestrian volumes. Only one of the most dangerous intersections for pedestrians was downtown. Noah Radford and David R. Ragland, "s.p.a.ce Syntax: An Innovative Pedestrian Volume Modeling Tool for Pedestrian Safety," U.C. Berkeley Traffic Safety Center, Paper UCB-TSC-RR-2003-11, December 11, 2003. Available at vol. 9 (2003), pp. 20509. The "safety in numbers" effect has been found in many other studies as well. For example, Noah Radford and David Ragland of the University of California at Berkeley looked at the city of Oakland, California. They found that nearly all of the city's most dangerous intersections were on the city's east side, an area with low pedestrian volumes. Only one of the most dangerous intersections for pedestrians was downtown. Noah Radford and David R. Ragland, "s.p.a.ce Syntax: An Innovative Pedestrian Volume Modeling Tool for Pedestrian Safety," U.C. Berkeley Traffic Safety Center, Paper UCB-TSC-RR-2003-11, December 11, 2003. Available at http://www.repositories.cdlib.org/its/tsc/UCB-TSC-RR-2003-11.

the slower they drive: See Kenneth Todd, "Pedestrian Regulations in the United States: A Critical Review," Transportation Quarterly, Transportation Quarterly, vol. 46, no. 4 (October 1992), pp. 54159. vol. 46, no. 4 (October 1992), pp. 54159.

for a longer period: The Danish transportation planner Jan Gehl makes this point in his seminal book Life Between Buildings Life Between Buildings (New York: Van Nostrand Reinhold, 1986), p. 79. (New York: Van Nostrand Reinhold, 1986), p. 79.

safest place to be a cyclist: Conversation with Dan Burden.

asked to remember something: A. M. Glenberg, J. L. Schroeder, and D. A. Robertson, "Averting the Gaze Disengages the Environment and Facilitates Remembering," Memory & Cognition, Memory & Cognition, vol. 26 (July 1998), pp. 65158. vol. 26 (July 1998), pp. 65158.

thought to aid memory: See A. Parker and N. Dagnall, "Effects of Bilateral Eye movements on Gist Based False Recognition in the DRM Paradigm," Brain and Cognition, Brain and Cognition, vol. 63, no. 3 (April 2007), pp. 22125. vol. 63, no. 3 (April 2007), pp. 22125.

other things, like driving: M. A. Recarte and L. M. Nunes, "Effects of Verbal and Spatial-Imagery Tasks on Eye Fixations While Driving," Journal of Experimental Psychology: Applied, Journal of Experimental Psychology: Applied, vol. 6, no. 1 (2000), pp. 3143. vol. 6, no. 1 (2000), pp. 3143.

on our mental workload: See, for example, M. C. Lien, E. Ruthruff, and D. Kuhns, "On the Difficulty of Task Switching: a.s.sessing the Role of Task-Set Inhibition," Psychonomic Bulletin & Review, Psychonomic Bulletin & Review, vol. 13 (2006), pp. 53035. vol. 13 (2006), pp. 53035.

for us to process things: C. Spence and L. Read, "Speech Shadowing While Driving: On the Difficulty of Splitting Attention Between Eye and Ear," Psychological Science, Psychological Science, vol. 14 (2003), pp. 25156. vol. 14 (2003), pp. 25156.

consumes even more effort: Curiously, this has not been studied extensively per se in driving simulator studies, but the work of Nilli Lavie, at the Inst.i.tute of Cognitive Neuroscience at University College London, and her colleagues hints at the problem. In a study, subjects were asked to perform a "linguistic task" that was either "high load" or "low load" when the task was low load, they were more likely to notice an irrelevant display of motion than when it was high load. Her finding-that people are unable to ignore irrelevant irrelevant stimuli when their "perceptual load" is not fully taxed, carries, as she mentioned to me in a conversation, the reverse implication that relevant stimuli will be less likely to be noticed under high-load conditions. See G. Rees, C. D. Frith, and N. Lavie, "Modulating Irrelevant Motion Perception by Varying Attentional Load in an Unrelated Task," stimuli when their "perceptual load" is not fully taxed, carries, as she mentioned to me in a conversation, the reverse implication that relevant stimuli will be less likely to be noticed under high-load conditions. See G. Rees, C. D. Frith, and N. Lavie, "Modulating Irrelevant Motion Perception by Varying Attentional Load in an Unrelated Task," Science, Science, vol. 278 (1997), pp. 161619. In more recent research, Lavie found that people engaged in intensive visual tasks were less likely to notice sounds at a low volume. It is not difficult to extrapolate from this that an intensive auditory task-for example, straining to hear a voice at low volume on a cell phone-will exact more pressure on the "perceptual load" and thus reduce performance in performing visual tasks. vol. 278 (1997), pp. 161619. In more recent research, Lavie found that people engaged in intensive visual tasks were less likely to notice sounds at a low volume. It is not difficult to extrapolate from this that an intensive auditory task-for example, straining to hear a voice at low volume on a cell phone-will exact more pressure on the "perceptual load" and thus reduce performance in performing visual tasks.

they still remembered fewer: David L. Strayer and Frank A. Drews, "Mult.i.tasking in the Automobile," in Attention: From Theory to Practice, Attention: From Theory to Practice, ed. A. Kramer, D. Wiegmann, and A. Kirlik (New York: Oxford University Press, 2006). ed. A. Kramer, D. Wiegmann, and A. Kirlik (New York: Oxford University Press, 2006).

When first asked this question: This is drawn from a conversation with Benjamin Coifman.

100 miles per hour: Robert Winkler, "The Need for Speed," New York Times, New York Times, November 13, 2005. November 13, 2005.

sequential "frames": Tim Andrews and Dale Purves, "The Wagon Wheel Illusion in Continuous Light, Trends in Cognitive Neuroscience, Trends in Cognitive Neuroscience, vol. 9, no. 6 (2005), pp. 26163. vol. 9, no. 6 (2005), pp. 26163.

demonstration of motion parallax): Mark Nawrot provided me with a simple exercise in "seeing" motion parallax at work: "For example, pick out two objects, near and far, on your desktop. Hold up your two index fingers, near to your face, one below the objects pointing up, one above pointing down. Hold your fingers stationary, fixate on the 'near' object, close one eye, and move your head side to side. Easy. Now do the same as you move your top finger along with your head movement so that it 'matches' the distant object. If you had to guess, you'd now say your top finger is farther away than your lower finger." For further interesting research on the mechanics of motion parallax, see Mark Nawrot, "Eye Movements Provide the Extra-retinal Signal Required for the Perception of Depth from Motion Parallax," Vision Research, Vision Research, vol. 43 (2003), pp. 155362. vol. 43 (2003), pp. 155362.

more realistic: In the scene in The Lord of the Rings The Lord of the Rings in which the "beacons" are being lit to sound the alarm for the impending danger to Rohan, the aerial camera sweeps across the landscape, but the beacon remains in the center of the shot as the background sweeps by. Nawrot suggests that the motion might trigger an involuntary "optokinetic response." To prevent us from simply being visually swept up in that background movement, however, the eye responds with a "smooth pursuit" movement to effectively countermand the motion and maintain the fixation on the lit beacon. This, Nawrot posits, mimics the series of compensatory eye movements we are constantly making in real life. Mark Nawrot and Chad Stockert, "Motion Parallax in Motion Pictures: The Role of Background Motion and Eye Movements" (unpublished paper, Department of Psychology, North Dakota State University). For a further fascinating discussion on human vision and the movies, see James E. Cutting, "Perceiving Scenes in Film and in the World," in in which the "beacons" are being lit to sound the alarm for the impending danger to Rohan, the aerial camera sweeps across the landscape, but the beacon remains in the center of the shot as the background sweeps by. Nawrot suggests that the motion might trigger an involuntary "optokinetic response." To prevent us from simply being visually swept up in that background movement, however, the eye responds with a "smooth pursuit" movement to effectively countermand the motion and maintain the fixation on the lit beacon. This, Nawrot posits, mimics the series of compensatory eye movements we are constantly making in real life. Mark Nawrot and Chad Stockert, "Motion Parallax in Motion Pictures: The Role of Background Motion and Eye Movements" (unpublished paper, Department of Psychology, North Dakota State University). For a further fascinating discussion on human vision and the movies, see James E. Cutting, "Perceiving Scenes in Film and in the World," in Moving Image Theory: Ecological considerations, Moving Image Theory: Ecological considerations, ed. J. D. Anderson and B. F. Anderson (Carbondale: Southern Illinois University Press, 2005), pp. 927. ed. J. D. Anderson and B. F. Anderson (Carbondale: Southern Illinois University Press, 2005), pp. 927.

"illusory pavement markings": Actually, any any pavement marking is rather illusory. pavement marking is rather illusory.

reduced their speed: "Evaluation of the Converging Chevron Pavement Marking Pattern," AAA Foundation for Traffic Safety (Washington, D.C.), July 2003.

have been mixed: "A Review of Two Innovative Pavement Marking Patterns That Have Been Developed to Reduce Traffic Speeds and Crashes," AAA Foundation for Traffic Safety (Washington, D.C.), August 1995.

at the higher speed: G. G. Denton, "The Influence of Adaptation on Subjective Velocity for an Observer in Simulated Rectilinear Motion," Ergonomics, Ergonomics, vol. 19 (1976), pp. 40930. vol. 19 (1976), pp. 40930.

sensation of moving backward: In a study by Stuart Anstis, subjects asked to jog on a treadmill for as little as a minute experienced this aftereffect. Once the treadmill was stopped, subjects asked to jog in place actually jogged, on average, 162 centimeters forward. forward. Anstis notes, "The backward motion of the treadmill produces an artificial mismatch between motor output and normal postural feedback, for which the adaptation compensates or nulls out by adjusting internal gain parameters to bring output and feedback back into line. But once the runner steps on to solid ground these newly adjusted parameters are now inappropriate and manifest themselves as an aftereffect, which dissipates as the parameters automatically update to match the solid ground. So these new aftereffects reveal the continuous neural recalibration of the gait control system." See Stuart Anstis, "Aftereffects from Jogging," Anstis notes, "The backward motion of the treadmill produces an artificial mismatch between motor output and normal postural feedback, for which the adaptation compensates or nulls out by adjusting internal gain parameters to bring output and feedback back into line. But once the runner steps on to solid ground these newly adjusted parameters are now inappropriate and manifest themselves as an aftereffect, which dissipates as the parameters automatically update to match the solid ground. So these new aftereffects reveal the continuous neural recalibration of the gait control system." See Stuart Anstis, "Aftereffects from Jogging," Experimental Brain Research, Experimental Brain Research, vol. 103 (1995), pp. 47678. vol. 103 (1995), pp. 47678.

when asked to speed up: For an excellent discussion of this issue see John Groeger, Understanding Driving Understanding Driving (East Suss.e.x, Psychology Press: 2001), p. 14. (East Suss.e.x, Psychology Press: 2001), p. 14.

largely, it is thought: This theory is credited to the pioneering work of J. J. Gibson, who wrote: "The aiming point of any locomotion is the center of the centrifugal flow of the ambient optic array." Gibson, The Ecological Approach to Visual Perception The Ecological Approach to Visual Perception (Boston: Houghton Mifflin, 1979), p. 182. The "steering" process is much more complicated than this, as we must somehow compensate, like Steadicams, for the fact that our eyes and heads are also moving as we move. For a good discussion of some of these complexities, see William H. Warren, "Perception of Heading Is a Brain in the Neck," (Boston: Houghton Mifflin, 1979), p. 182. The "steering" process is much more complicated than this, as we must somehow compensate, like Steadicams, for the fact that our eyes and heads are also moving as we move. For a good discussion of some of these complexities, see William H. Warren, "Perception of Heading Is a Brain in the Neck," Nature Neuroscience, Nature Neuroscience, vol. 1, no. 8 (1998), pp. 64749. Warren also provides the example of the vol. 1, no. 8 (1998), pp. 64749. Warren also provides the example of the Millennium Falcon Millennium Falcon in hypers.p.a.ce to describe the radial pattern away from the focus of expansion. in hypers.p.a.ce to describe the radial pattern away from the focus of expansion.

"global optical flow": Not all of our sense of motion comes from visual inputs, of course. The reason I, like many other people, experienced bouts of "simulator sickness" in the various driving simulators in which I drove is that the picture of the moving road I was looking at did not correspond to what my vestibular system (the "balance" system of the inner ear) was experiencing.

our "target": In an interesting experiment at Brown University, researchers used virtual reality to create an optically impossible situation in which subjects had to walk toward something without the use of optical flow, instead of merely walking toward the object via its egocentric direction (its direction in s.p.a.ce relative to the subject). Subjects were less accurate in their approach without the optic flow. See W. H. Warren, Bruce Kay, Wendy Zosh, Andrew Duchon, and Stephanie Sahue, "Optic Flow Is Used to Control Human Walking," Nature Neuroscience, Nature Neuroscience, vol. 4, no. 2 (2001), pp. 21316. vol. 4, no. 2 (2001), pp. 21316.

a kind of radial pattern: This is not an entirely resolved issue and is still being debated. Gibson, for example, observed: "The behavior involved in steering an automobile, for instance, has usually been misunderstood. It is less a matter of aligning the car with the road than it is a matter of keeping the focus of expansion in the direction one must go." But as vision researcher Michael Land has pointed out, this argument may not account for a driver's behavior around curves: "On a curved trajectory the locations of the stationary points in the flow-field vary with distance, generating a curved line across the ground plane, not a single focus of expansion." Land notes that we rely instead of the inner edge of the road in driving around curves, with some 80 percent of driver's glances being directed in that region. See Michael F. Land, "Does Steering a Car Involve Perception of the Velocity Flow Field?" in Motion VisionComputational, Neural, and Ecological Constraints, Motion VisionComputational, Neural, and Ecological Constraints, ed. Johannes M. Zanker and Jochen Zeil (New York: Springer Verlag, 2001). ed. Johannes M. Zanker and Jochen Zeil (New York: Springer Verlag, 2001).

our sense of speed: It has also been argued that optic flow influences our estimates of distance while driving as well. See M. Lappe, A. Grigo, F. Bremmer, H. Frenz, R. J. V. Bertin, and I. Israel, "Perception of Heading and Driving Distance from Optic Flow," Driving Simulation Conference 2000 Driving Simulation Conference 2000 (Paris), pp. 2531. (Paris), pp. 2531.

tree-lined roads: This information comes from T. Triggs, "Speed Estimation," in Automotive Engineering and Litigations, Automotive Engineering and Litigations, vol. 2, ed. G. A. Peters and B. Peters (New York: Garland Law Publishing), pp. 56998. vol. 2, ed. G. A. Peters and B. Peters (New York: Garland Law Publishing), pp. 56998.

flow at the same speed: Christopher Wickens, Engineering Psychology and Human Performance Engineering Psychology and Human Performance (Upper Saddle River, N.J.: Prentice Hall, 2000), p. 162. (Upper Saddle River, N.J.: Prentice Hall, 2000), p. 162.

those at lower heights: See, for example, Christina M. Rudin-Brown, "The Effect of Driver Eye Height on Speed Choice, Lane-Keeping, and Car-Following Behavior: Results of Two Driving Simulator Studies," Traffic Injury Prevention, Traffic Injury Prevention, vol. 7, no. 4 (December 2006), pp. 36572; or B. R. Fajen and R. S. David, "Speed Information and the Visual Control of Braking to Avoid a Collision," vol. 7, no. 4 (December 2006), pp. 36572; or B. R. Fajen and R. S. David, "Speed Information and the Visual Control of Braking to Avoid a Collision," Journal of Vision, Journal of Vision, vol. 3, no. 9 (2003), pp. 555555a. vol. 3, no. 9 (2003), pp. 555555a.

than they intend to: See C. M. Rudin-Brown, "Vehicle Height Affects Drivers' Speed Perception: Implications for Rollover Risk," Transportation Research Record No. 1899: Driver and Vehicle Simulation, Human Performance, and Information Systems for Highways; Railroad Safety; and Visualization in Transportation Transportation Research Record No. 1899: Driver and Vehicle Simulation, Human Performance, and Information Systems for Highways; Railroad Safety; and Visualization in Transportation (Washington, D.C.: National Research Council, 2004), pp. 8489. (Washington, D.C.: National Research Council, 2004), pp. 8489.

speed more than others: See, for example, Allan F. Williams, Sergey Y. Kyrchenko, and Richard A. Retting, "Characteristics of Speeders," Journal of Safety Research, Journal of Safety Research, vol. 37 (2006), pp. 22732. Of course, any findings that drivers of SUVs and pickups drove faster than other vehicles brings up other "confounding" factors, such as a higher rate of male drivers for those vehicle categories, or the idea that people who choose to drive SUVs and pickups may be more p.r.o.ne to speeding or feel safer and thus are more likely to drive at a higher speed-instead of the vehicle making them more p.r.o.ne to speeding. vol. 37 (2006), pp. 22732. Of course, any findings that drivers of SUVs and pickups drove faster than other vehicles brings up other "confounding" factors, such as a higher rate of male drivers for those vehicle categories, or the idea that people who choose to drive SUVs and pickups may be more p.r.o.ne to speeding or feel safer and thus are more likely to drive at a higher speed-instead of the vehicle making them more p.r.o.ne to speeding.

slowly than they really were: N Harre, "Discrepancy Between Actual and Estimated Speeds of Drivers in the Presence of Child Pedestrians," Injury Prevention, Injury Prevention, vol. 9 (2003), pp. 3841. vol. 9 (2003), pp. 3841.

slow down slightly: See "Research Shows Speed Trailers Improve Safety in Temporary Work Zones," Texas Transportation Researcher, Texas Transportation Researcher, vol. 36, no. 3 (2000). vol. 36, no. 3 (2000).

Some highway agencies: Minnesota Tailgating Pilot Project Minnesota Tailgating Pilot Project (St. Paul, Mn: Department of Public Safety, 2006). The Pac-Man information comes from the (St. Paul, Mn: Department of Public Safety, 2006). The Pac-Man information comes from the Star Tribune, Star Tribune, December 20, 2006. December 20, 2006.

how fast they're going: For a good roundup of research, see Leonard Evans, Traffic Safety Traffic Safety (Bloomfield Hills, Mich.: Science Serving Society, 2004), p. 173. (Bloomfield Hills, Mich.: Science Serving Society, 2004), p. 173.

279 feet: I am using the example provided by crash investigator and human factors researcher Marc Green, available at http://www.visualexpert.com/Resources/reactiontime.htm.

directly at a fielder: For a fascinating discussion of the complexities of catching a ball, among other things, see Mike Stadler, The Psychology of Baseball The Psychology of Baseball (New York: Gotham Books, 2007). (New York: Gotham Books, 2007).

as much as several seconds: Robert Dewar and Paul Olson note that drivers "often perceive a stationary vehicle as moving, even with five seconds' viewing." Dewar and Olson, Human Factors in Traffic Safety Human Factors in Traffic Safety (Tuscon: Lawyers and Judges Publishing, 2002), p. 23. (Tuscon: Lawyers and Judges Publishing, 2002), p. 23.

no idea of the rate: For a good discussion of this, see Olson and Farber, Forensic Aspects of Driver Perception and Response Forensic Aspects of Driver Perception and Response (Tucson: Lawyers and Judges Publishing Co., 2003), p. 112. (Tucson: Lawyers and Judges Publishing Co., 2003), p. 112.

overtaking crashes: The psychologists Rob Gray and David Regan suggest that what is going on here is that as we stare for a while at things like the white stripes on the road, or trees on the side of the road, our brains quickly adapt; they compare the effect to the well-known "waterfall effect": You stare at water rushing down a waterfall for a while, and then look at a nearby rock-it will seem to be moving upward. When we come off the highway, something similar happens, and it may look to us as if the stop sign at the end of the ramp is farther away than it really is, which is why engineers have tested chevrons and other patterns on off-ramps: to break up the illusion of those white stripes. Rob Gray and David Regan, "Risky Driving Behavior: A Consequence of Motion Adaptation for Visually Guided Motor Action," Journal of Experimental Psychology: Human Perception and Performance, Journal of Experimental Psychology: Human Perception and Performance, vol. 26, no. 6 (2000), pp. 172132. vol. 26, no. 6 (2000), pp. 172132.

really tell the difference: This has long been known to people who study driving. In Human Limitations in Automobile Driving Human Limitations in Automobile Driving (Garden City: Doubleday, Doran & Company, 1938), authors J. R. Hamilton and Louis L. Thurstone (psychologists at Harvard University) observed: "From eight hundred feet right down to where the other car is almost on top of you, the average eye will not have any idea of the (Garden City: Doubleday, Doran & Company, 1938), authors J. R. Hamilton and Louis L. Thurstone (psychologists at Harvard University) observed: "From eight hundred feet right down to where the other car is almost on top of you, the average eye will not have any idea of the rapidity rapidity of motion, or speed, of the oncoming car. It will perceive motion, and that is all. The distance at which motion is first perceived, as we have said above, does not depend very much on the speed of either car. of motion, or speed, of the oncoming car. It will perceive motion, and that is all. The distance at which motion is first perceived, as we have said above, does not depend very much on the speed of either car. But the distance at which rapidity of motion is perceived depends entirely upon the speed of each car. But the distance at which rapidity of motion is perceived depends entirely upon the speed of each car. [italics in original] With two cars traveling 40 miles an hour, that distance where the average eye suddenly perceives rapidity of motion is about 145 feet between cars. When two cars are traveling at 50 miles an hour, that distance is about 70 feet. Now we begin to have some understanding of the reason for the frightful collision accidents on the highway." [italics in original] With two cars traveling 40 miles an hour, that distance where the average eye suddenly perceives rapidity of motion is about 145 feet between cars. When two cars are traveling at 50 miles an hour, that distance is about 70 feet. Now we begin to have some understanding of the reason for the frightful collision accidents on the highway."

speed of the opposing car: See D. A. Gordon and T. M. Mast, "Driver's Decisions in Overtaking and Pa.s.sing," Highway Research Record, Highway Research Record, no. 247, Highway Research Board, 1968. no. 247, Highway Research Board, 1968.

your attempted pa.s.sing: One study remarked on a "conundrum" about pa.s.sing difficulty and pa.s.sing risk, noting that drivers were found "to be somewhat poor at making the judgments required for pa.s.sing maneuvers, particularly judgments about opposing vehicle speed, but the safety record of pa.s.sing maneuvers is very good. This suggests that pa.s.sing maneuvers occur in a relatively forgiving environment. First, while drivers are relatively poor in making pa.s.sing judgments, many drivers may inherently understand this and make very conservative decisions about pa.s.sing. Second, the buffer area provided downstream of each pa.s.sing zone provides a margin of safety against collisions resulting from poor driver judgments." From "Pa.s.sing Sight Distance Criteria," NCHRP Project 15-26, MRI Project 110348, prepared for the National Cooperative Highway Research Program, Transportation Research Board National Research Council, Midwest Research Inst.i.tute, March 2000.

up by only 30 percent: L. Staplin, "Simulator and Field Measure of Driver Age Differences in Left-Turn Gap Judgments," Transportation Research Board Record, Transportation Research Board Record, no. 1485, Transportation Research Board, National Research Council, 1995. no. 1485, Transportation Research Board, National Research Council, 1995.

to actually see: R. E. Eberts and A. G. MacMillan, "Misperception of Small Cars," in Trends in Ergonomics/Human Factors, Trends in Ergonomics/Human Factors, vol 2, ed. R. E. Ebert and C. G. Eberts (North Holland: Elsevier Science Publishers, 1985). vol 2, ed. R. E. Ebert and C. G. Eberts (North Holland: Elsevier Science Publishers, 1985).

slower the object seems: H. W. Leibowitz, "Grade Crossing Accidents and Human Factors Engineering," American Scientist, American Scientist, vol. 73, no. 6 (NovemberDecember 1985), pp. 55862. Leibowitz also noted another potential reason-the "deceptive geometry of collisions"-for overestimating the distance of an approaching train, similar to the problem mentioned with drivers trying to judge the distance of an approaching car. A car and a train that are approaching each other will retain consistent positions. He wrote, "There is no lateral motion, and thus the princ.i.p.al cue to velocity is the increase in size of the visual angle subtended or the expansion pattern.... The rate of increases of the expansion pattern is not linear but rather is described by a hyperbolic function. For distant objects, the rate of change in the expansion is low. As the distance decreases, the visual angle subtended increases at an accelerated rate." This is somewhat similar to a phenomenon known as "motion camouflage," which has been observed in the natural world-male hoverflies, for example, move in a way to conceal the fact that they are moving when they are tracking female hoverflies. They do so, it has been argued, by "approaching along a path such that its image projected onto the prey's eye emulates that of a distant stationary object (a vol. 73, no. 6 (NovemberDecember 1985), pp. 55862. Leibowitz also noted another potential reason-the "deceptive geometry of collisions"-for overestimating the distance of an approaching train, similar to the problem mentioned with drivers trying to judge the distance of an approaching car. A car and a train that are approaching each other will retain consistent positions. He wrote, "There is no lateral motion, and thus the princ.i.p.al cue to velocity is the increase in size of the visual angle subtended or the expansion pattern.... The rate of increases of the expansion pattern is not linear but rather is described by a hyperbolic function. For distant objects, the rate of change in the expansion is low. As the distance decreases, the visual angle subtended increases at an accelerated rate." This is somewhat similar to a phenomenon known as "motion camouflage," which has been observed in the natural world-male hoverflies, for example, move in a way to conceal the fact that they are moving when they are tracking female hoverflies. They do so, it has been argued, by "approaching along a path such that its image projected onto the prey's eye emulates that of a distant stationary object (a fixed point fixed point). During its attack, the predator must ensure that it is always positioned directly between the current position of the prey and this fixed point." Humans, research has suggested, are also susceptible to this effect. See Andrew James Anderson and Peter William McOwan, "Humans Deceived by Predatory Stealth Strategy Camouflaging Motion," Proceedings of the Royal Society B: Biological Sciences, Proceedings of the Royal Society B: Biological Sciences, vol. 270, Supp. 1 (August 7, 2003), pp. S18S20. vol. 270, Supp. 1 (August 7, 2003), pp. S18S20.

latter was moving faster: Joseph E. Barton and Theodore E. Cohn, "A 3D Computer Simulation Test of the Leibowitz Hypothesis," U.C. Berkeley Traffic Safety Center, Paper UCB-TSC-TR-2007-10, April 1, 2007; http://repositories.cdlib.org/its/tsc/UCB-TSC-TR-2007-10.

human vision is an illusion: See Sandra J. Ackerman, "Optical Illusions: Why Do We See the Way We Do?" HHMI Bulletin, HHMI Bulletin, June 2003, p. 37. June 2003, p. 37.

(much more at night): Dewar and Olson, Human Factors in Traffic Safety Human Factors in Traffic Safety, p. 88.

remember more at night): D. Shinar and A. Drory, "Sign Registration in Daytime and Night Time Driving," Human Factors, Human Factors, vol. 25 (1983), pp. 11722. vol. 25 (1983), pp. 11722.

blind to our blindness: See H. W. Leibowitz, "Nighttime Driving Accidents and Selective Visual Degradation," Science, Science, vol. 197 (July 29, 1977), pp. 42223. vol. 197 (July 29, 1977), pp. 42223.

as drivers actually do: M. J. Allen, R. D. Hazlett, H. L. Tacker, and B. L. Graham, "Actual Pedestrian Visibility and the Pedestrian's Estimate of His Own Visibility," American Journal of Optometry and Archives of the American Academy of Optometry, American Journal of Optometry and Archives of the American Academy of Optometry, vol. 47 (1970), pp. 4449, and David Shinar, "Actual Versus Estimated Night-time Pedestrian Visibility," vol. 47 (1970), pp. 4449, and David Shinar, "Actual Versus Estimated Night-time Pedestrian Visibility," Ergonomics, Ergonomics, vol. 27, no. 8 (1984), pp. 86371, and Richard Tyrrel, Joanne Wood, and Trent Carberry, "On-road Measures of Pedestrians' Estimates of Their Own Nighttime Conspicuity," vol. 27, no. 8 (1984), pp. 86371, and Richard Tyrrel, Joanne Wood, and Trent Carberry, "On-road Measures of Pedestrians' Estimates of Their Own Nighttime Conspicuity," Journal of Safety Research, Journal of Safety Research, vol. 35, no. 5 (December 2004), pp. 48390. vol. 35, no. 5 (December 2004), pp. 48390.

drive 20 miles per hour: See Olsen, Forensic Aspects of Driver Perception and Response, Forensic Aspects of Driver Perception and Response, p. 157. p. 157.

through the landscape: The contrast experiment discussed can be viewed at http://www.psy.ucsd.edu/~sanstis/Foot.htm. For an interesting discussion of the experiment and the traffic implications, see Stuart Anstis, "Moving in a Fog: Contrast Affects the Perceived Speed and Direction of Motion," Proceedings of the Conference on Neural Networks, Proceedings of the Conference on Neural Networks, Portland, Ore., 2003. Portland, Ore., 2003.

signs have been set up: See C. Arthur MacCarley, Christopher Ackles, and Tabber Watts, "A Study of the Response of Highway Traffic to Dynamic Fog Warning and Speed Advisory Messages," TRB 06-3086, Transportation Research Record, National Research Council, Washington, D.C., February 2007.

not brake accordingly: For an excellent discussion of snowplow visibility, see Albert Yonas and Lee Zimmerman, "Improving the Ability of Drivers to Avoid Collisions with Snowplows in Fog and Snow," Minnesota Department of Transportation, St. Paul, Minn., July 2006.

glances over the shoulder: The rearview mirror information is drawn from Thomas Ayres, Li Li, Doris Trachtman, and Douglas Young, "Pa.s.senger-Side Rear-View Mirrors: Driver Behavior and Safety," International Journal of Industrial Ergonomics, International Journal of Industrial Ergonomics, vol. 35 (2005), pp. 15762. vol. 35 (2005), pp. 15762.

actually it is half: half: This example was proposed by the art historian E. H. Gombrich in This example was proposed by the art historian E. H. Gombrich in Art and Illusion Art and Illusion (Oxford: Phaidon Press, 1961) and was later confirmed and studied further by Marco Bertamini and Theodore E. Parks in "On What People Know About Images on Mirrors," (Oxford: Phaidon Press, 1961) and was later confirmed and studied further by Marco Bertamini and Theodore E. Parks in "On What People Know About Images on Mirrors," Cognition, Cognition, vol. 98 (2005), pp. 85104. Their use of the phrase "on mirrors" immediately reveals one of the disconnects we tend to have with mirrors, as we tend to say "in mirrors," as if the image lurked behind the gla.s.s. The authors note, "Both the fact that our image is half the physical size, and the fact that this relationship is independent of how far we are from the mirror, are counterintuitive. However, they become clearer as soon as we realize that a mirror is always located halfway between oneself and our virtual self." vol. 98 (2005), pp. 85104. Their use of the phrase "on mirrors" immediately reveals one of the disconnects we tend to have with mirrors, as we tend to say "in mirrors," as if the image lurked behind the gla.s.s. The authors note, "Both the fact that our image is half the physical size, and the fact that this relationship is independent of how far we are from the mirror, are counterintuitive. However, they become clearer as soon as we realize that a mirror is always located halfway between oneself and our virtual self."

"they ought to be": For details on Flannagan's work with rearview mirrors, see M. J. Flannagan, M. Sivak, J. Schumann, S. Kojima, and E. Traube, "Distance Perception in Driver-Side and Pa.s.senger-Side Convex Rearview Mirrors: Objects in Mirror are More Complicated Than They Appear," Report No. UMTRI-97-32, July 1997.

Chapter Four: Why Ants Don't Get into Traffic Jams.

"cricket war": William G. Harley, "Mormons, Crickets, and Gulls: A New Look at an Old Story," Utah Historical Quarterly, Utah Historical Quarterly, vol. 38 (Summer 1970), pp. 22439. vol. 38 (Summer 1970), pp. 22439.

"black carpet": From Peter Calamai, "Crickets March with Religious Fervor," Toronto Star, Toronto Star, August 2, 2003. August 2, 2003.

as a tight swarm: A good way to think about this in human terms, as complex-systems theorist Eric Bonabeau has cleverly done, is to imagine a c.o.c.ktail party. Each person in the room is given a command: Pick two people at random, A and B, and then place yourself so that A is constantly between B and you. In a room of people, this results in a loose crowd always on the move, shifting to stay in the right position, some people at times drifting around the periphery like timid wallflowers. Now change the rules, however, so that you you are always between A and B. Instead of milling, the crowd will clump into a "single, almost stationary cl.u.s.ter." A seemingly minor change in the way each person acts completely alters the group. Could you have predicted that? From Eric Bonabeau, "Predicting the Unpredictable," are always between A and B. Instead of milling, the crowd will clump into a "single, almost stationary cl.u.s.ter." A seemingly minor change in the way each person acts completely alters the group. Could you have predicted that? From Eric Bonabeau, "Predicting the Unpredictable," Harvard Business Review, Harvard Business Review, vol. 80, no. 3 (March 2002). For a more in-depth discussion of the dynamics involved, see Bonabeau, Pablo Funes, and Belinda Orme, "Exploratory Design of Swarms," vol. 80, no. 3 (March 2002). For a more in-depth discussion of the dynamics involved, see Bonabeau, Pablo Funes, and Belinda Orme, "Exploratory Design of Swarms," Proceedings of the Second International Workshop on the Mathematics and Algorithms of Social Insects Proceedings of the Second International Workshop on the Mathematics and Algorithms of Social Insects (Atlanta, GA: Georgia Inst.i.tute of Technology, 2003), pp. 1724. (Atlanta, GA: Georgia Inst.i.tute of Technology, 2003), pp. 1724.

to play by the rules: Matt Steingla.s.s made an important point while writing about a collision that Seymour Papert, the founder of MIT's Artificial Intelligence Lab, suffered with a motorbike while crossing the street in Hanoi, Vietnam, a city where the traffic behavior is as much explained by "emergent behavior" as it is by formal traffic rules (if not more so): "One thing about emergent phenomena that the pioneers of the field tended not to emphasize is that they are often unkind to their const.i.tuent agents: Ant colonies are not very solicitous of the lives of individual ants. Hanoi traffic is a fascinating emergent phenomenon, but it didn't take good care of Seymour Papert when he became one of its const.i.tuent agents." Steingla.s.s, "Caught in the Swarm," Boston Globe, Boston Globe, December 17, 2006. December 17, 2006.

the "wrong" direction: For a fascinating discussion of the dynamics of the wave, see I. Farkas, D. Helbing, and T. Vicsek, "Mexican Waves in an Excitable Medium," Nature, Nature, vol. 419 (2002), pp. 13132. For a simulation and videos, see vol. 419 (2002), pp. 13132. For a simulation and videos, see www.angel.elte.hu/wave/.

none died: Gregory A. Sword, Patrick D. Lorch, and Darryl T. Gwynne, "Migratory Bands Give Crickets Protection," Nature, Nature, vol. 433 (February 17, 2005). vol. 433 (February 17, 2005).

a congested mess: This recalls a number of studies of how animal behavior changes under increasingly crowded conditions. A study that looked at cats found results that sound a lot like rush-hour freeways: "The more crowded the cage is, the less relative hierarchy there is. Eventually a despot emerges, 'pariahs' appear, driven to frenzy and all kinds of neurotic behavior by continuous and pitiless attack by all others; the community turns into a spiteful mob. They all seldom relax, they never look at ease, and there is a continuous hissing, growling, and even fighting. Play stops altogether and locomotion and exercises are reduced to a minimum." Quoted in E. O. Wilson, Sociobiology: The New Synthesis Sociobiology: The New Synthesis (Cambridge, Ma.s.s.: Harvard University Press, 1995), p. 255. (Cambridge, Ma.s.s.: Harvard University Press, 1995), p. 255.

difference in the number of cars: David Shinar and Richard Compton, "Aggressive Driving: An Observational Study of Driver, Vehicle, and Situational Factors," Accident a.n.a.lysis & Prevention, Accident a.n.a.lysis & Prevention, vol. 36 (2004), pp. 42937. vol. 36 (2004), pp. 42937.

road signs and white stripes: The biologist E. O. Wilson notes that "in general, it appears that the typical ant colony operates with somewhere between 10 and 20 signals, and most of these are chemical in nature." E. O. Wilson and Bert Holldobler, The Ants The Ants (Cambridge, Ma.s.s.: Havard University Press, 1990), p. 227. (Cambridge, Ma.s.s.: Havard University Press, 1990), p. 227.