Quantitative Analysis of the Responses of V1 Neurons to Horizontal Disparity in Dynamic Random-Dot Stereograms

Abstract

Quantitative analysis of the responses of V1 neurons to horizontal disparity in dynamic random-dot stereograms. J Neurophysiol 87: 191-208, 2002; 10.1152/jn.00465.2000. Horizontal disparity tuning for dynamic random-dot stereograms was investigated for a large population of neurons (n ϭ 787) in V1 of the awake macaque. Disparity sensitivity was quantified using a measure of the discriminability of the maximum and minimum points on the disparity tuning curve. This measure and others revealed a continuum of selectivity rather than separate populations of disparity-and nondisparity-sensitive neurons. Although disparity sensitivity was correlated with the degree of direction tuning, it was not correlated with other significant neuronal properties, including preferred orientation and ocular dominance. In accordance with the Gabor energy model, tuning curves for horizontal disparity were adequately described by Gabor functions when the neuron's orientation preference was near vertical. For neurons with orientation preferences near to horizontal, a Gaussian function was more frequently sufficient. The spatial frequency of the Gabor function that described the disparity tuning was weakly correlated with measurements of the spatial frequency and orientation preference of the neuron for drifting sinusoidal gratings. Energy models make several predictions about the relationship between the response rates to monocular and binocular dot patterns. Few of the predictions were fulfilled exactly, although the observations can be reconciled with the energy model by simple modifications. These same modifications also provide an account of the observed continuum in strength of disparity selectivity. A weak correlation between the disparity sensitivity of simultaneously recorded single-and multiunit data were revealed as well as a weak tendency to show similar disparity preferences. This is compatible with a degree of local clustering for disparity sensitivity in V1, although this is much weaker than that reported in area MT. I N T R O D U C T I O NSelectivity for binocular disparity was initially demonstrated using elongated bar stimuli in cat area 17 (Barlow et al. 1967;Pettigrew et al. 1968) and V1 of the awake monkey (Poggio and Fischer 1977). Subsequently, Poggio and colleagues (Poggio 1995;Poggio et al. 1985Poggio et al. , 1988 examined the sensitivity to horizontal disparity in random-dot stereograms (RDS) in macaque V1. None of the studies using RDS has attempted to describe the disparity tuning quantitatively. Consequently, there has been no quantitative analysis of the relationship between disparity selectivity to RDS and other fundamental properties of V1 neurons, such as orientation tuning and ocular dominance.There are several reasons why it is important to study these issues with RDS. First, a change in the disparity of a bar stimulus also generates changes in the monocular images, which by themselves may influence neuronal firing. By contrast the monocular images of random-dot stimuli are spatially homogeneous. There...

Sensitivity to relative disparity in early visual cortex of pigmented and albino ferrets

“…The Gaussian has a half width at half height (HWHH) of 3.95° of visual angle. Abscissa horizontal relative disparity in degrees of visual angle Prince et al 2002). We modulated horizontal disparity Wrst in coarse, then in Wner steps of 2°, 1°, 0.5°, and 0.25°.…”

“…The exact mechanisms underlying stereopsis, however, are still unknown and have been a matter of discussion for years (e.g. DeAngelis et al 1995;Ohzawa et al 1996Ohzawa et al , 1997Anzai et al 1997;Bridge et al 2001;Prince et al 2002;Nienborg et al 2004).…”

“…The fourth group, the tuned-inhibitory cells, responds optimally to objects at all disparities except those near zero. Although it is argued that especially the three groups of excitatory neurons may not be discrete (LeVay and Voigt 1988;Prince et al 2002), application of this classiWcation appears to be beneWcial for Wnding diVerences of the response proWles between categories (Poggio 1995). Thus, this classiWcation is still commonly used, but it should be emphasized that the early visual areas code for the whole range of disparities.…”

Disparity processing in primary visual cortex

“…In the classic BEM, the shape of the monocular RF largely determines the shape of the disparity tuning curve [37]. For example, if the monocular RFs are Gabors, the disparity tuning will also be a Gabor, and its parameters are determined by the parameters of the monocular RFs.…”

“…No published study has explicitly examined this question for disparity-selective neurons. We therefore re-examined data from neurons recorded in previously published studies [37,45,46] Figure 5. The distribution of responses to different random dot patterns in the BEM.…”