Elsevier

Vision Research

Volume 33, Issue 4, March 1993, Pages 447-462
Vision Research

Dissociation of discrimination thresholds for time to contact and for rate of angular expansion

https://doi.org/10.1016/0042-6989(93)90252-RGet rights and content

Abstract

It is well known that, if a rigid sphere is moving at constant speed towards the eye along the line of sight then, for small values of θ, T = θ/gq, where T is the time to contact, θ is the instantaneous angular size and θ is the rate of increase of angular size. We describe a rationale and an experimental procedure for demonstrating empirically when subjects base discrimination of time to contact on trial-to-trial variations of (θ/θ) rather than on variations of θ or on variations of Δθ (the change of angular size during a presentation). Discrimination threshold for the ratio (θ/θ) was 0.070–0.13, and was independent of mean time to contact over a range of at least T = 1.0–4.0 sec. We conclude that the human visual pathway contains a mechanism that is sensitive to the ratio (θ/θ) rather independently of the values of θ and θ. Using a different procedure we demonstrated empirically that subjects based discriminations of rate of expansion on trial-to-trial variations of θ rather than variations of time to contact or on variations of Δθ. Discrimination threshold for rate of expansion was 0.85-0.14, and was independent of mean time to contact over a range of at least T = 1.0−4.0 sec. We conclude that the human visual pathway contains a mechanism that is sensitive to rate of expansion rather independently of time to contact or absolute change in size. When rate of expansion and time to contact were both available as cues, discrimination threshold was on average lower than when only one of the two cues was present. We conclude that there is some summation of the two cues. Our data can be explained by a small modification to a model previously put forward to account for data on threshold elevations and aftereffects caused by adapting to changing-size stimulation. This model incorporates a filter that is strongly activated by isotropic, homogeneous two-dimensional expansion of the retinal image and whose output is inversely proportional to time to contact (i.e. the more urgent the demand for evasive action, the stronger the output of the filter).

Reference (49)

  • BeverleyK.I. et al.

    Visual sensitivity to the shape and size of a moving object: Implications for models of object perception

    Perception

    (1980)
  • BeverleyK.I. et al.

    Device for measuring the precision of eye-hand coordination while tracking changing-size

    Aviation, Space and Environmental Medicine

    (1980)
  • BeverleyK.I. et al.

    Texture changes versus size changes as stimuli for motion in depth

    Vision Research

    (1983)
  • BlakemoreC. et al.

    On the existence of neurons within the human visual system selectively sensitive to the orientation and size of retinal images

    Journal of Physiology, London

    (1971)
  • BootsmaR.J. et al.

    Timing an attacking forehand drive in table tennis

    Journal of Experimental Psychology: Human Perception and Performance

    (1990)
  • CavalloV. et al.

    Visual information and skill level in time-to-collision estimation

    Perception

    (1988)
  • CollewijnH. et al.

    Binocular eye movements and the perception of depth

  • De ValoisR.L. et al.

    Spatial vision

    Annual Review of Psychology

    (1980)
  • GottsdankerR.M.

    The ability of human operators to detect acceleration of target motion

    Psychological Bulletin

    (1956)
  • GottsdankerR.M. et al.

    Identifying the acceleration of visual targets

    British Journal of Psychology

    (1961)
  • GreenB.A.

    Vector calculus

    (1967)
  • HoyleF.

    The black cloud

  • KaufmanL.

    Sight and mind

  • KrukR. et al.

    Visual test results compared with flying performance in telemetry-tracked aircraft

    Aviation. Space and Environmental Medicine

    (1983)

    • Cited by (0)

    This research was presented in part to the Sixth International Conference on Event Perception and Action, Amsterdam, 1991 and to the Association for Research in Vision and Ophthalmology (ARVO), Sarasota, Fla, 1992 [ Investigative Ophthalmology and Visual Science (Suppl.), 33, 1138].

    View full text
    Copyright © 1993 Published by Elsevier Ltd.