Factors influencing velocity coding in the human visual system

Human velocity and direction discrimination measured with random dot patterns

“…set '. These findings are in agreement with the hypothesis formulated in our previous studies (Orban et al, 1984(Orban et al, , 1986Orban, 1985), that cortical cells which operate as bandpass filters for velocity (velocity tuned cells) and cortical cells which are selective for the direction of motion, as described in areas 17 and 18 of the cat (Orban et al,198 la,b) and in area V5 of the monkey (Zeki, 1978;Maunsell and Van Essen, 1983) underly the short range process of human motion perception. Indeed these populations of cells respond maximally at intermediate speeds (Orban et al, 1981a, b;Maunsell and Van Essen, 1983).…”

“…The thresholds we observed are in agreement with those reported in other studies (McKee, 198 1;McKee and Welch, 1985;Ball and Sekuler, 1987) and correspond to the results obtained in our previous studies (Orban et al, 1984(Orban et al, , 1986. It is interesting to note that the velocity and direction differences needed for a clear segregation by motion (van Doorn and Koenderink, 1983) are extremely large compared with the local velocity and direction resolution levels.…”

“…1983) our linking hypothesis predict a U-shaped relationship between JNDs in velocity, expressed as Weber fractions, and stimulus velocity. This U-shaped relationship has been observed in humans (Orban et al, 1984). cats (Vandenbussche et al, 1986a) and monkeys (Vandenbussche et al, 1986b).…”

“…The second requirement follows from the observation that JNDs do not depend on other parameters than the one to be discriminated, while cortical cell's activity at an early level, depends on many visual parameters. In a previous study we compared velocity discrimination and opposed motion discrimination for a moving light bar (Orban et al, 1984). However these two tests not only differ in visual parameters discriminated but also in psychophysical tasks.…”

Visual short-term memory of stimulus velocity in patients with unilateral posterior brain damage

“…Neuropsychological studies of patients with bilateral or unilateral posterior brain damage suggest the existence an analogous area in the extrastriate human cortex that subserves the processing of image motion (Zihl et al, 1983(Zihl et al, , 1991Newcombe et al, 1987;Vaina, 1989;. Healthy human observers can correctly discriminate small differences in the velocity of moving targets (Notterman and Page, 1957;Brandalise and Gottsdanker, 1959;Mandriota et al, 1962;McKee, 1981;Orban et al, 1984), and this precision can be maintained despite random variations in the contrast and spatial frequency of the grating stimuli (McKee et al, 1986). In addition, stimulus velocity can also be stored in visual short-term memory for durations up to 10 set without loss of precision (Magnussen and Greenlee, 1992).…”