Article Figures & Data
Figures
- Figure 1.
Fine disparity discrimination task and psychophysical performance. A, The monkey was first required to fixate a spot located at the center of the display; then a random-dot stereogram was presented for 1.5 s over the receptive field. The size of the center patch was matched to the receptive field size. The monkey had to maintain fixation until 0.5 s after the offset of the visual stimulus. The fixation point then disappeared, and the monkey made a saccade to one of the two targets to indicate whether the center patch was perceived as nearer or farther than the surrounding annulus. The disparity of the center patch (center disparity) was varied from trial to trial, whereas that of the surrounding annulus (surround disparity) was fixed at 0° except in training and generalization test sessions. Top views of the stimulus and the observer are shown in the insets in Stimulus On. B, Psychometric functions, in which the proportion of far choices is plotted as a function of center disparity. Each data point is the average proportion across all single-unit recording sessions (Monkey R, n = 53; Monkey K, n = 35). Error bars indicate SDs. The vertical dashed line represents the surround disparity.
- Figure 2.
Psychophysical performance in generalization test sessions. A, Psychophysical performance of Monkey R on a generalization test session in which trials with RDSs of untrained surround disparities (±0.2°; filled symbols) were interleaved with trials with RDSs of trained surround disparities (0°, ±0.4°; open symbols). In trials with untrained surround disparities, rewards were delivered on a random half of the trials. Axis conventions are the same as in Figure 1B. B, Psychophysical thresholds for untrained (filled symbols) and trained (open symbols) surround disparities calculated from the data shown in A. Circles represent the thresholds estimated by the model that assumes the lapse rate of zero; squares represent the thresholds estimated by the model that includes the lapse rate as a free parameter. C, The points of subjective equalities (PSEs) plotted against the surround disparity for untrained (filled symbols) and trained (open symbols) stimuli. D–F, Psychophysical performance in another generalization test session in which surround disparities of ±0.1° were used as untrained surround disparities.
- Figure 3.
Neurometric and psychometric functions for two example experiments. A, The disparity-tuning curve of a V4 neuron while the animal performed a fixation task. Symbols and error bars represent mean firing rates and SEM, respectively. The horizontal dashed line represents spontaneous firing rate. The vertical dashed line represents the surround disparity (0°). B, The disparity-tuning curve of the same neuron while the animal performed the fine disparity discrimination task. Conventions are as in A. Note that the error bars were smaller than the symbols. C, The performance of the neuron on the discrimination task, quantified using receiver operating characteristics analysis, is plotted as a function of center disparity (filled symbols) together with the performance of the monkey (open symbols). Solid and dashed curves show the fitted cumulative Gaussian functions for the neuron and the monkey, respectively. The horizontal dashed line indicates the chance level. D–F, An example of a V4 neuron that was less sensitive than the monkey.
- Figure 4.
Relationship between neuronal and psychophysical thresholds for 88 neurons. The diagonal is the identity line. Upper right, Distribution of neuronal to psychophysical threshold ratios. Neurons whose neuronal thresholds were larger than 10 are plotted at the rightmost end of the scatter plot (n = 6).
- Figure 5.
Covariation between responses of a V4 neuron and behavioral choices was assessed on a trial-by-trial basis. Each panel shows the histograms of firing rates for each center disparity, grouped according to the monkey's choice (filled bars, near choice trials; open bars, far choice trials). For each panel, the center disparity and the choice probability (CP; if calculated) are shown at the upper left and right, respectively.
- Figure 6.
Mean choice probability across 88 neurons as a function of signed center disparity (positive- and negative-signed disparities indicate preferred and null disparities, respectively). Error bars indicate SDs. There are no error bars for the leftmost point because only one data point was available for the center disparity. The dashed line represents the chance level of choice probability (0.5).
- Figure 7.
Distribution of grand choice probabilities for 88 neurons. Filled bars indicate neurons whose grand choice probability was significantly different from 0.5 (permutation test, p < 0.05).
- Figure 8.
Time course of choice-predictive activity for the neurons with grand choice probabilities significantly larger than 0.5 (n = 27). Values on the abscissa indicate the center of the bin. A, For each disparity, the mean firing rates binned at 20 ms were normalized to the maximum firing rate. Normalized firing rates were then averaged across disparities for each neuron, followed by averaging across neurons. The solid and dashed black lines represent mean normalized responses for preferred and null choices, respectively. The gray line indicates the difference in normalized responses between preferred and null choice trials. Only stimulus conditions in which the monkey chose one target in no more than 75% of the trials were included in the analysis. B, Time course of the average grand choice probability across neurons calculated with 100 ms bins. Solid line and shaded areas represent the mean and SEM, respectively. The dashed line indicates the grand choice probability of 0.5.
- Figure 9.
Effects of eye movements and dot-pattern variations on choice probabilities. A, Grand choice probabilities calculated from the residuals of the linear regression of neuronal responses on vergence angle are plotted against those without correction for vergence angle (original grand choice probabilities) from the two monkeys (n = 85). Three neurons were excluded from this analysis because we monitored movements of only one eye during the recording of these neurons. B, Grand choice probabilities corrected for vertical eye movement were plotted against the original grand choice probabilities (n = 85). C, Grand choice probabilities corrected for horizontal eye movement plotted against the original grand choice probabilities (n = 85). D, Choice probabilities calculated from trials in which dot patterns were identical across trials were plotted against those calculated from trials in which dot patterns were varied from trial to trial for 31 neurons from Monkey R. These stimuli consisted of the center patch at zero disparity and were randomly interleaved in trials with a nonzero disparity center patch.
- Figure 10.
Relationship between neuronal thresholds and grand choice probabilities. Grand choice probabilities are plotted against neuronal thresholds (n = 88). Neurons whose neuronal thresholds were larger than 10 are plotted at the rightmost end of the scatter plot (n = 6).
- Figure 11.
Effects of microstimulation for two example stimulation sites in V4 of Monkey R. A, The disparity-tuning curve of multiunit activity at a near-preferring site. Conventions are the same as in Figure 2A. B, Effects of microstimulation of the near-preferring site. Proportion of far choices is plotted as a function of center disparity for the trials with (filled circles) and without (open circles) microstimulation. Each data point is based on 40 trials. A logistic regression model was fitted to produce psychometric curves for trials with (solid line) and without (dashed line) microstimulation conditions. The horizontal and vertical dashed lines indicate the proportion of far choice of 0.5 and the surround disparity, respectively. C, The disparity-tuning curve of multiunit activity at a far-preferring site. D, Effects of microstimulation of the far-preferring site.
- Figure 12.
Distribution of microstimulation effects for 31 sites from Monkey R. The magnitude of microstimulation effects was quantified as the horizontal shift of the center of the psychometric curve in units of degree. Positive values indicate that the direction of the shift was consistent with the disparity preference of multiunit activity at the stimulation site. The filled bars indicate sites where microstimulation elicited a significant shift of the psychometric curve (Wald test, p < 0.05).
Tables
- Table 1.
Logistic regression coefficients for the two example microstimulation experiments
Variable β SE p value The example near site (Fig. 11A,B) Constant 0.85 (β0) 0.17 <0.0001 Center disparity 141 (β1) 17 <0.0001 Microstimulation −0.85 (β2) 0.23 0.00019 Center disparity × microstimulation 18 (β3) 25 0.49 The example far site (Fig. 11C,D) Constant −1.57 (β0) 0.22 <0.0001 Center disparity 187 (β1) 22 <0.0001 Microstimulation 1.50 (β2) 0.27 <0.0001 Center disparity × microstimulation −31 (β3) 29 0.28
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