T. E Cohn

University of California, Berkeley

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Thanh Hung Nguyen

Hanoi University of Science and Technology

J. Barton

UNSW Sydney

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Hanoi University of Science and Technology

IT University of Copenhagen

Tokyo Institute of Technology

Administration for Community Living

American Jewish Committee

Viet Nam University Of Traditional Medicine

University of Defence

Geospatial Research (United Kingdom)

RIKEN Center for Advanced Intelligence Project

Mongolia International University

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A visual factor in rear-end collisions?

Journal of Vision (2010)

T. E Cohn Thanh Hung Nguyen J. Barton

In the US, over 20% of collisions between automobiles are rear-end collisions. But for transit buses, whose exposure and pattern of movement may be quite different, the number is significantly higher, being over 35%. If buses are more susceptible to this type of collision than automobiles, one wonders why. In this report we describe both a property of human vision that may relate to the answer plus a theory as to the link. Some formulations of the visual task inherent in avoiding such collisions suggest that an observer may utilize the angular width of an object ahead, divided by its time rate of change, to calculate a time to collision (TTC). Consider the initial act of perceiving closure with a vehicle ahead. If the quotient of angular width to its time derivative is what is used to initiate braking, then it must be done accurately. We have discovered that the time to react (RT) to a step increase in angular width is seen more slowly the larger the object. The stimulus contained only the 2D cue to closure and depth of field was unchanged at 1.5 m. Objects were light gray squares set in a dark gray surround. The size change started at a random time after a ready signal and was effected gradually, averaging close to a pixel per MSEC in 13.3 MSEC steps. Six normal observers were employed. Average reaction time (2 s.e.) were 284.5 (1.65) MSEC for 3.7 DEG, 294.2 (1.69) MSEC for 5.3 DEG, and 296.5 (1.80) MSEC for 7.6 DEG. The effect is small, about 10% of the estimated perceptual delay, but it is significant. Suppose that the computation of the time derivative of width, dw/dt, is thus distorted by an elevated dt. This lowers dw/dt and thus raises TTC. This finding accords with a conjecture by Leibowitz to explain collisions where trains strike vehicles. He suggested that larger objects appear to move more slowly, damaging the accuracy of the required TTC computation. His conjecture may also apply to collisions between automobiles.

Stimulus (psychology)

10.1167/3.9.214

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Specifying the Appearance of Escalator Treads: How to Minimize the Disorientation Effect

T. E Cohn

Escalator passengers sometimes experience a feeling of disorientation or dizziness while boarding or riding the machine. Prior work has shown that this perception may be due to a visual depth illusion caused by the appearance of the escalator tread. Measurements confirm that the escalator tread surface is a highly periodic visual stimulus exhibiting unusually high contrast as well as a spatial frequency matched to the preferences of the visual nervous system. Means of minimizing the depth illusion are explored. These center on disrupting the periodic structures of the tread surface. Expressions intended to serve as candidates for figure of merit for the tread appearance are developed. These take into account some properties of the visual nervous system including the decline with eccentricity of visual acuity and the bandpass character of spatial detail processing under light adapted conditions.

10.1520/stp18348s

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