B Gulyas

Response latencies of visual cells in macaque areas V1, V2 and V5

The response to moving light and dark slits was recorded from a total of 94 cells in V1, V2, and V5 (MT) in 9 anesthetized and paralyzed macaque monkeys (M. fascicularis). Using the spatial lag method2, response latencies were calculated for each cell. We obtained median latencies of 85, 96, and 94 ms for cells in areas V1, V2, and V5, respectively. The higher median latencies of V2 and V5 cells compared to V1 are commensurate with later stages of information processing, and are predictable from the anatomy of the interconnections. In addition, a distinct, second population of high-latency cells is present in all 3 regions, but is most abundant in lamina 4 of V5. These may represent either external feedback from other regions or ongoing processing. Extensive overlap of latencies in all 3 regions at both the high and low ends of their respective ranges indicates a considerable degree of parallel interaction between striate and extrastriate cortex.

Corticofugal feedback influences the responses of geniculate neurons to moving stimuli

SummaryGeniculate cell responses to moving bars and moving texture were compared in normal cats and in cats in which the corticofugal feedback was removed by cortical ablation. In experimental animals the response strength and the velocity upper cutoff assessed with a moving bar was reduced compared to control animals. The strength of response to texture decreased even more after cortical ablation, which also changed the response pattern of X cells to moving texture. These data suggest that corticofugal feedback contributues to the geniculate responses to moving stimuli and in particular to moving texture.

Temporal integration in cat visual cortex: A test of bloch's law

Some units in the cat visual cortex fail to respond to a briefly flashed bar and it has been suggested that such neurons function as visual integrators with a long time constant. To test this integrator hypothesis, a study was made using presentations of a bar, flashed over the receptive field for various durations and at different luminances. Some cortical cells indeed showed an increase in the time to peak latency and in the response amplitude when stimulus duration was prolonged up to 320 msec. Such units obeyed Blochs law for durations over 100 msec.

Influence of moving textured backgrounds on responses of cat area 18 cells to moving bars.

Publisher Summary This chapter extends the study to area 18 of the cat. The chapter reveals the influence of moving textured backgrounds on responses of cat area 18 cells to moving bars. Area 18 of the cat is considered to be a second primary area and has been implicated in the analysis of moving objects. Comparison of the interactions in areas 17 and 18 should reveal further differences between these areas and could, therefore, further test the hypothesis that area 17 is involved in the analysis of stationary objects and area 18 in the analysis of moving objects. Most neurophysiological studies on mechanisms involved in motion analysis have used a single stimulus such as a moving bar, grating, or random dot pattern. The visual world in which humans, monkeys, and cats live is far more complex than these simple stimuli. In addition, the direction selectivity of striate neurons was strongly modulated by background motion giving rise to six different relative direction selectivity types.

Responses of cat striate neurons to moving light and dark bars: changes with eccentricity

Responses of area-17 neurons to light and dark bars moving over a wide range of speeds were measured over a range of receptive-field locations in anesthetized and paralyzed cats. For both light bars and dark bars, velocity sensitivity shifted to higher speeds with increasing eccentricity, whereas response strength and direction selectivity hardly changed. The good correlation between response strength and velocity sensitivity for light and dark bars suggests that ON and OFF inputs converge upon most area-17 cells. The correlation between direction selectivities for light and dark bars was not better than that between velocity sensitivities for light and dark bars. Only cells with strong direction selectivity were equally direction selective for light bars and dark bars. Comparison with previous studies done with high-contrast stimuli shows that the shift in sensitivity to higher speeds with increasing eccentricity is contrast dependent.