Visual sensitivity to temporal modulations of temporal noise.
The present endeavor is meant (a) to provide a direct comparison between first- and second-order temporal modulation and, by so doing, (b) to eliminate all spatial clues that might have contaminated previous assessments of the second-order temporal modulation transfer function (TMTF). The second aim was achieved by means of the temporal modulation of a purely temporal white noise, a stimulus used frequently in psychoacoustics but not used as yet in visual stimulation. Luminance and contrast temporal modulation thresholds were measured with a 2AFC staircase procedure. In the first case, the mean luminance of a spatially homogeneous, 30 degrees field was modulated sinusoidally over time (first-order modulation). In the second case, the luminance of the same or of a 60 degrees field was randomized over time at a rate of 150 Hz and this temporal white noise (the carrier) was modulated sinusoidally over time (second-order modulation). First-order thresholds reproduce the classical (large field) flicker sensitivity. Second-order thresholds (measured for the first time with purely temporal stimuli) are at least 100 times higher than first-order ones, display a low-pass characteristic (at least up to 0.5 Hz) and yield a critical fusion frequency (measured at 100% modulation) of approximately 10 Hz. The data are in accord with other estimates of the TMTF of the second-order system and thus confirm the effective neutralization of the spatial cues present in these previous studies.
Gorea
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A
Laboratoire de Psychologie Expérimentale, C.N.R.S. and René Descartes University, 71 Avenue Edouard Vaillant, 92774, Boulogne Billancourt, France. gorea@psycho.univ.paris5.fr
Wardak
C
C
Lorenzi
C
C
D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D008029:Lighting; D008297:Male; D010775:Photic Stimulation; D011601:Psychophysics; D014795:Visual Pathways / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*