1990), they do not consider image features, but instead compute the interocular cross-correlation between left and right images.
Because current models of binocular processing are based on cross-correlation between the left and right eyes ( Ohzawa et al. Thereafter, Read and Cumming (2018) proposed that the mixed-polarity benefit could arise from subtle changes in image correlation that can occur in some circumstances. Recently, Goncalves and Welchman (2017) showed that it is possible to capture the mixed-polarity benefit using a simple linear-nonlinear processing architecture that does not depend on separate ON and OFF channels. However, the convergence of ON and OFF channels in V1 to form simple cells ( Schiller 1992) seems to contradict this as a potential explanation for the mixed-polarity benefit. 1978) and are maintained at the retinal ganglion and lateral geniculate nucleus level as ON and OFF center cells. Separate of ON and OFF channels first appear at the bipolar cell level as ON and OFF ganglia ( Nelson et al. Such neural infrastructure would reduce the number of potential binocular matches in a mixed-polarity stimulus, i.e., a random-dot stereogram (RDS), by as much as half, simplifying the stereoscopic correspondence problem considerably. This “mixed-polarity benefit” was originally explained on the basis that bright and dark features are processed by separate ON and OFF channels ( Harris and Parker 1995). A clue to understanding the neural computation of binocular stereopsis may be found in the observation that depth judgements are more accurate when binocular images are composed of both light and dark features, rather than just one or the other ( Harris and Parker 1995).
It remains an important challenge to understand how the brain combines a pair of 2-D retinal images to support 3-D perception. These results indicate that excitation and inhibition facilitate processing of single- and mixed-polarity stereograms in the early visual cortex to different extents.īinocular stereopsis is one of the primary cues for three-dimensional (3-D) vision. Using magnetic resonance spectroscopy, we show that adult human participants’ Glx concentration is significantly higher whereas GABA concentration is significantly lower in the early visual cortex when participants view mixed-polarity random-dot stereograms (RDS) compared with single-polarity RDS. NEW & NOTEWORTHY Depth judgements are better when images comprise both light and dark features, rather than only light or only dark elements. These results indicate that excitation and inhibition facilitate processing of single- and mixed-polarity stereograms in the early visual cortex to different extents, consistent with recent theoretical work (Goncalves NR, Welchman AE. We find that participants’ Glx concentration is significantly higher, whereas GABA concentration is significantly lower, when mixed-polarity RDS are viewed than when single-polarity RDS are viewed. In particular, we use magnetic resonance spectroscopy to measure Glx and GABA concentrations in the early visual cortex of adult humans during viewing of single- and mixed-polarity random-dot stereograms (RDS). Motivated by this discovery, we seek to test the potential for changes in the balance of excitation and inhibition that are produced by viewing these stimuli. Goncalves and Welchman ( Curr Biol 27: 1403–1412, 2017) observed that single- and mixed-polarity stereograms evoke different levels of positive and negative activity in a deep neural network trained on natural images to make depth judgements, which also showed the mixed-polarity benefit. Since Harris and Parker ( Nature 374: 808–811, 1995) discovered the “mixed-polarity benefit,” there has been limited evidence supporting their hypothesis that the benefit is due to separate bright and dark channels. It was previously shown that depth judgements are better when images comprise both light and dark features, rather than only light or only dark elements. The offset between images projected onto the left and right retina (binocular disparity) provides a powerful cue to the three-dimensional structure of the environment.
0 kommentar(er)
