Why Is It Easier to Identify Someone Close Than Far Away?

Article excerpt

It is a matter of common sense that a person is easier to recognize when close than when far away. A possible explanation for why this happens begins with two observations. First, the human visual system, like many image-processing devices, can be viewed as a spatial filter that passes higher spatial frequencies, expressed in terms of cycles/degree, progressively more poorly. Second, as a face is moved farther from the observer, the face's image spatial frequency spectrum, expressed in terms of cycles/face, scales downward in a manner inversely proportional to distance. An implication of these two observations is that as a face moves away, progressively lower spatial frequencies, expressed in cycles/face-and therefore, progressively coarser facial details-are lost to the observer at a rate that is likewise inversely proportional to distance. We propose what we call the distance-as-filtering hypothesis, which is that these two observations are sufficient to explain the effect of distance on face processing. If the distance-as-filtering hypothesis is correct, one should be able to simulate the effect of seeing a face at some distance, D, by filtering the face so as to mimic its spatial frequency composition, expressed in terms of cycles/face, at that distance. In four experiments, we measured face perception at varying distances that were simulated either by filtering the face as just described or by shrinking the face so that it subtended the visual angle corresponding to the desired distance. The distance-as-filtering hypothesis was confirmed perfectly in two face perception tasks: assessing the informational content of the face and identifying celebrities. Data from the two tasks could be accounted for by assuming that they were mediated by different low-pass spatial filters within the human visual system that have the same general mathematical description but that differ in scale by a factor of approximately 0.75. We discuss our results in terms of (1) how they can be used to explain the effect of distance on visual processing, (2) what they tell us about face processing, (3) how they are related to "flexible spatial scale usage," as discussed by Schyns and colleagues, and (4) how they may be used in practical (e.g., legal) settings to demonstrate the loss of face information that occurs when a person is seen at a particular distance.

PROLOGUE

In the year 1997, October 10 was the day on which the citizens of Alaska received their annual oil dividend of approximately $1,500 per person. Perhaps it was to celebrate this event that four young hoodlums decided to hit the streets of Fairbanks for a Clockwork-Orange-style evening of vicious attacks on random individuals. When the night was over, a teenage boy, identified as L.H., lay dead, and an older man, Franklin Dayton, was seriously injured as a result of the gang's marauding.

Fairbanks, Alaska is not a town that takes violent events in stride: The public responded in outrage, and police reaction was swift. Within days, four suspects were arrested and locked up. Eventually, they were tried for the crimes.

At trial, the prosecutor introduced various kinds of evidence bearing on the defendants' guilt. However, the prosecutor had no smoking gun, literal or metaphorical, and the centerpiece of his case was an eyewitness account provided by one Arlo Olson. Mr. Olson testified that while standing in the doorway of Eagles Hall in downtown Fairbanks, he had watched in horror as a group of men, whom he later identified as the defendants, accosted and savagely beat Mr. Dayton in a parking lot a couple of blocks away.

Of some note is that "a couple of blocks away"-the distance from Olson's vantage point to the parking lot-was determined to be approximately 450 ft. In response to this and related issues, the defense flew in an expert witness from Seattle-a psychologist whose job was to educate the jury about various pitfalls of human perception and memory. …