Intraocular recordings from brisk-sustained and brisk-transient ganglion cells in the cat's retina revealed a systematic increase in center size and decrease in spatial cut-off frequency with increasing distance from the area centralis. At any one eccentricity sizes of the centers of sustained and transient cells did not overlap, and the variation in cut-off frequency for each class was constrained to about one-half octave.

1. The statistical correlation of detection thresholds for pairs of stimuli should be higher for stimuli detected by the same mechanism than for stimuli detected by different mechanisms‐‐a property that can be used to probe the visual mechanisms that underlie detection. 2. Correlation of contrast sensitivities for pairs of spatiotemporal stimuli is approximately a linear function of spatial or temporal frequency separation in octaves. Using the slope of this function as an index of neural processing gave results consistent with: more spatial mechanisms than temporal; more spatial mechanisms at low temporal frequencies than at high; and at least two temporal mechanisms active at spatial frequencies up to 22.6 cycles deg‐1. 3. This method of analysing sensitivity data is insensitive to experimental conditions and applicable to any sensory detection task mediated by tuned channels. In addition to being applicable to psychophysical sensitivity measurements, it may also be useful in analysing some kinds of electrophysiological measurements that pool the responses from many active mechanisms (such as evoked potentials).

No abstract

Response histograms were collected for brisk-sustained and brisk-transient ganglion cells in the cat retina as narrow bars were moved backwards and forwards across their receptive fields. When a bar of fixed length was moved across the centre of the receptive field with contrast proportional to velocity, a constant response was obtained as long as the centre of the receptive field was crossed within the summation time. However, if the length of the bar was such that it extended beyond the centre, then there was a small but steady increase in surround antagonism for an increase in velocity. The same response was produced by a brief whole-field flash as by an extended bar moving across the receptive field at high velocity if both stimulus conditions delivered the same energy uniformly across the receptive field. With brisk-sustained cells it was observed, for small bar lengths, that bar length and contrast could be exchanged to give a constant response, even when there was considerable non-linearity in the over-all stimulus-response relationship. Thus conditions that resulted in constant stimulus flux produced a constant response. This property was seen at both high and low velocities for the majority of brisk-sustained units. The stimulus-response relationship had a greater range of linearity at high velocities than at low velocities. From similar experiments with brisk-transient cells it was observed that bar length and contrast could only be exchanged to give a constant response at high velocities. At low velocities there was considerable non-linearity: there appeared to be saturation of the response from local regions and it was necessary to extend the bar outside such a region to obtain an increase in response. At lower velocities, despite the changes seen in length-response curves under different conditions of contrast and velocity, the degree of surround antagonism remained constant for a given cell. Further, both brisk-sustained and brisk-transient cells showed the same degree of surround antagonism.

SUMMARY1. Extracellular recording of the responses of cat retinal ganglion cells to narrow moving bars revealed systematic response variations with changes in stimulus velocity. These response variations were studied by collecting peri-stimulus histograms from brisk-sustained (X) and brisk-transient (Y) ganglion cells as narrow elongated bars were moved backwards and forwards across their receptive fields.2. Velocity-response curves were produced from plots of the amplitude of the main peak of the histograms as a function of velocity. The shape of these curves was found to be reasonably constant for both classes of ganglion cells.3. For a given cell, the peak of the velocity-response curve shifted to both a higher response level and a higher velocity as the stimulus contrast was increased.4. Within both classes of cells there was a systematic shift in the velocity-response curve as a function of the size of the receptive field centre. For brisk-sustained cells this was seen as an increase in both the response and velocity at the peak for larger centre sizes, while for brisk-transient cells it was an increase in velocity at the peak with negligible change in response.5. When the velocity required to produce a small criterion response was determined, there were distinct differences between the two classes of cells. When plotted on a double-logarithmic scale as a function of centre size the brisk-sustained cells had a slope of 200 while brisk-transient cells had a slope of 1-20.6. Within the area centralis brisk-transient cells responded more readily at high velocities than brisk-sustained cells. This was not the case in the peripheral retina, where both cell classes responded about equally at high velocities.