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Directional tuning properties of 89 neurones sampled in the visual wulst. (A-D) Responses of two representative direction-selective neurones to 45% contrast sinusoidal gratings drifting at optimal spatial and temporal frequencies. Left panels: Responses are shown as average peristimulus time histograms (PSTHs) for 16 different stimulus directions (as indicated on top of each histogram) with 10 repeated measures at each using a randomized order of stimulus presentation (bin size ¼ 10 ms). Spontaneous activity was collected before the onset of the stimulus (first 500 ms of the PSTHs). Gratings were presented from 500 to 2500 ms, as indicated by the bars beneath the first column of PSTHs. The grey-shaded rectangles delineate the 1800 ms period considered for the analyses, after the exclusion of the 200 ms period following stimulus onset. Right panels: Direction tuning curves in which mean firing rate (spikes ⁄ s), computed over the whole stimulation period minus the initial 200 ms, is plotted as a function of stimulus direction. The open circles indicate mean response amplitude in the preferred and antipreferred direction. Solid lines represent the fitted models used to determine the half width at half height of the model peak response, which was our measure of the cell's directional tuning bandwidth (BW). Bars indicate the confidence interval of the mean at the 95% level. The models were based on the sum of two von Mises functions, as described in Materials and methods. The grey horizontal line indicates the level of spontaneous activity. (E) Distribution of direction indices (DIs). The DI has positive values that increase from 0 to 1 as mean response in the preferred direction increase relative to that in the antipreferred direction, with values above 1 if the response is inhibited (below spontaneous activity level). The dashed line indicates the boundary between orientation-selective (DI < 0.5) and direction-selective (DI ‡ 0.5) neurones. (F) Distribution of direction bandwidths. Mean and median values are represented for both DI and bandwidth distributions by the filled and empty triangles, respectively.

Directional tuning properties of 89 neurones sampled in the visual wulst. (A-D) Responses of two representative direction-selective neurones to 45% contrast sinusoidal gratings drifting at optimal spatial and temporal frequencies. Left panels: Responses are shown as average peristimulus time histograms (PSTHs) for 16 different stimulus directions (as indicated on top of each histogram) with 10 repeated measures at each using a randomized order of stimulus presentation (bin size ¼ 10 ms). Spontaneous activity was collected before the onset of the stimulus (first 500 ms of the PSTHs). Gratings were presented from 500 to 2500 ms, as indicated by the bars beneath the first column of PSTHs. The grey-shaded rectangles delineate the 1800 ms period considered for the analyses, after the exclusion of the 200 ms period following stimulus onset. Right panels: Direction tuning curves in which mean firing rate (spikes ⁄ s), computed over the whole stimulation period minus the initial 200 ms, is plotted as a function of stimulus direction. The open circles indicate mean response amplitude in the preferred and antipreferred direction. Solid lines represent the fitted models used to determine the half width at half height of the model peak response, which was our measure of the cell's directional tuning bandwidth (BW). Bars indicate the confidence interval of the mean at the 95% level. The models were based on the sum of two von Mises functions, as described in Materials and methods. The grey horizontal line indicates the level of spontaneous activity. (E) Distribution of direction indices (DIs). The DI has positive values that increase from 0 to 1 as mean response in the preferred direction increase relative to that in the antipreferred direction, with values above 1 if the response is inhibited (below spontaneous activity level). The dashed line indicates the boundary between orientation-selective (DI < 0.5) and direction-selective (DI ‡ 0.5) neurones. (F) Distribution of direction bandwidths. Mean and median values are represented for both DI and bandwidth distributions by the filled and empty triangles, respectively.

Contexts in source publication

Context 1
... pattern of directional responses during presentation of gratings is shown for two representative neurones in Fig. 2A and C. It can be observed in this figure that both neurones responded selectively to particular directions of motion, exhibiting sustained discharge rates throughout stimulus presentation after occasional initial transient components. These transient components were not considered for the main part of our analysis (the first 200 ms ...
Context 2
... tuning curves of the neurones whose responses are represented in Fig. 2A and C are plotted on a linear scale in Fig. 2B and D, respectively. We also show the fits that we applied to the tuning curves in order to estimate the directional tuning half-widths at halfmaximum response. As apparent in both examples, and true for the rest of our sample, the fits provided a good description of the data. Only six out ...
Context 3
... tuning curves of the neurones whose responses are represented in Fig. 2A and C are plotted on a linear scale in Fig. 2B and D, respectively. We also show the fits that we applied to the tuning curves in order to estimate the directional tuning half-widths at halfmaximum response. As apparent in both examples, and true for the rest of our sample, the fits provided a good description of the data. Only six out of 89 neurones had to be discarded for not ...
Context 4
... In other words, 91% of the data could be explained by the fits. The latter were based on the sum of two von Mises functions, whose parameters for peak positions, heights and widths were free. Such parameters could be adjusted to obtain adequate descriptions of the unimodal tuning profiles of strongly directional cells (DI value around 1, Fig. 2B), as well as the bimodal profiles of directional cells less strongly selective due to subsidiary peaks in the antipreferred direction (Fig. 2D). As a consequence of this, the higher peak of the fits, from which our estimates of bandwidths were derived, was always found around the preferred ...
Context 5
... for peak positions, heights and widths were free. Such parameters could be adjusted to obtain adequate descriptions of the unimodal tuning profiles of strongly directional cells (DI value around 1, Fig. 2B), as well as the bimodal profiles of directional cells less strongly selective due to subsidiary peaks in the antipreferred direction (Fig. 2D). As a consequence of this, the higher peak of the fits, from which our estimates of bandwidths were derived, was always found around the preferred ...
Context 6
... data of DIs and tuning bandwidths are presented as histograms in Fig. 2E and F, respectively. The strength of directional selectivity ranged from non-directional (DI ¼ 0.10) to strongly unidirectional, with suppression in relation to spontaneous activity in the antipreferred direction (DI ¼ 1.35). For the large subpopulation of direction-selective cells, DI values were concentrated around a mean of 0.9, ...
Context 7
... ¼ 1.35). For the large subpopulation of direction-selective cells, DI values were concentrated around a mean of 0.9, indicating a tendency towards unidirectionality without inhibition in the antipreferred direction, which was seen only in 20% of cells. The variability of tuning bandwidth values, which was apparent in the tuning curves shown in Fig. 2B and D, was reflected in the broad distribution shown in Fig. 2F (range 14.2-61.0°). The mean for the whole sample was 28.0° and roughly 45% of the cells had bandwidth values ranging between 20 and 30°. Values for directionally selective cells were not significantly different from those of nondirection-selective cells (27.8 ± 1.25° vs. ...
Context 8
... stimuli. In response to gratings drifting in 16 different directions through its receptive field, the first neurone (Fig. 3A) had a marked preference for the upward direction and the strength (DI ¼ 0.91) and narrowness of the bandwidth (BW ¼ 27.0°) of its directional tuning were typical of many direction-selective neurones in our data set (see Fig. 2A and B). In response to plaids (Fig. 3B), this neurone showed two peaks of activity at motion directions symmetrically opposite to one another by an angle of 45° with respect to the upward direction. This is what would be expected from a neurone that responds independently to each of the component gratings of 90° plaids. To verify this ...
Context 9
... of the observations made so far were based on analyses in which neuronal discharges occurring within the first 200 ms of stimulation were excluded. By doing so, we sought to minimize the potential contamination of activity not directly related to the motion direction of the stimuli. However, as exemplified in Fig. 2A and C, the presence of transient peaks of activity shortly after stimulus onset was mostly noticeable for stimuli moving at or near preferred and ⁄ or antipreferred directions, suggesting that these early responses are, at least to some extent, directionally selective. We therefore decided to examine the component ⁄ pattern motion ...

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