Motion detection from photopic to low scotopic luminance levels

• Published in: Vision research (Oxford) 2000, Vol.40 (2), p.187-199
• Main Authors: van de Grind, Wim A, Koenderink, Jan J, van Doorn, Andrea J
• Format: Article
• Language: English
• Subjects: Adaptation, Ocular - physiology; Adult; Biological and medical sciences; Female; Fundamental and applied biological sciences. Psychology; Humans; Luminance levels; Luminescent Measurements; Male; Middle Aged; Motion detection; Motion Perception - physiology; Perception; Photopic; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Scotopic; Sensory Thresholds - physiology; Space life sciences; Vision; Visual Acuity - physiology
• ISSN: 0042-6989; 1878-5646
• DOI: 10.1016/S0042-6989(99)00167-4

In this study we quantify the influence of adaptation luminance on the threshold for direction-detection in coherently moving random-pixel arrays (RPAs). Square RPAs of a constant rms-contrast (35%) were used and we determined their ‘critical’ or threshold-width W c. Mean retinal illuminances were varied in 13 steps of 0.5 log unit from the low photopic range (screen luminance 0.3 cd/m 2) down to 6 log units attenuation, which appeared to be about the absolute threshold of vision under the conditions of our experiment. Moving RPAs were presented at six retinal locations (0, 3, 6, 12, 24 and 48°) from the fovea to the far periphery in the temporal visual field of the right eye of three experienced observers (the authors). In order to ensure an honest comparison between these very disparate conditions, the spatial dimensions (including speed) were scaled according to the acuity, as measured separately for each of the viewing-conditions and observers. Acuity scaling proves to equate the performance for all eccentricities and luminance levels rather well. The fovea is special, but only in the sense that the absolute threshold for light detection is reached earlier than in peripheral regions. In all other respects foveal results follow the pattern found for peripheral locations. Two different regimes can be discerned in the data, one for high and one for low speeds. In the low speed range W c is almost constant, regardless of luminance level or eccentricity. The critical ‘crossing-time’ T c for any pixel starting at one end of the stimulus and leaving at the opposite end is therefore inversely proportional to velocity in the low-speed range (time–velocity reciprocity). At medium-to-high speeds W c increases linearly with velocity, so T c is constant. This constant (minimum) value of T c differs between subjects, but in all subjects it increases somewhat with decreasing luminance level, even for our acuity-scaled stimuli. The different behaviour for low and high speeds [reported before for photopic viewing conditions by van de Grind, W. A., van Doorn, A. J., & Koenderink, J. J. (1983. Journal of the Optical Society of America, 73, 1674–1683) and van de Grind, W. A., Koenderink, J. J., & van Doorn A. J. (1986. Vision Research, 26, 797–810)] proves to hold from photopic to low scotopic luminance ranges, provided the stimuli are scaled according to acuity. We draw the general conclusion that movement detection is a very robust process that tolerates extremely low r