PubMed · 7260025
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J Cooper, J Feldman. 1981. Depth perception in strabismus.. https://doi.org/10.1136/bjo.65.7.510
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The target in a visual search task usually pops out if it can be distinguished from its background on the basis of only one visual feature but not if the target represents a conjunction of two or more features. However, several recent reports suggest that in certain cases, search targets defined by a conjunction of two features also pop out. We have reinvestigated three pairs of such features to determine whether the popout in these cases can be attributed to perceptual grouping. We find that that in all three cases, popout no longer occurs when perceptual grouping is degraded, suggesting that the popout is the result of perceptual grouping and not of novel mechanism/s of conjunction search.
We view perceptual tasks such as vision and speech recognition as inference problems where the goal is to estimate the posterior distribution over latent variables (e.g., depth in stereo vision) given the sensory input. The recent flurry of research in independent component analysis exemplifies the importance of inferring the continuous-valued latent variables of input data. The latent variables found by this method are linearly related to the input, but perception requires nonlinear inferences such as classification and depth estimation. In this article, we present a unifying framework for stochastic neural networks with nonlinear latent variables. Nonlinear units are obtained by passing the outputs of linear gaussian units through various nonlinearities. We present a general variational method that maximizes a lower bound on the likelihood of a training set and give results on two visual feature extraction problems. We also show how the variational method can be used for pattern classification and compare the performance of these nonlinear networks with other methods on the problem of handwritten digit recognition.
Stereoscopic depth discrimination was investigated in crossed and uncrossed directions using stimuli defined by binocular disparity differences embedded in dynamic random-dot stereograms. Across three experiments, fixation was directed to a point on the display screen (which placed crossed stimuli in front of and uncrossed stimuli behind, the background dots of the stereogram), to a point in front of the display screen (which placed both crossed and uncrossed stimuli in front of the background dots), and to a point behind the display screen (which placed both crossed and uncrossed stimuli behind the background dots). Results showed that depth discrimination was always good when the stimuli appeared in front of the background dots of the stereogram, whereas discrimination was always poor when the stimuli appeared behind the background dots. These results suggest that differences between crossed and uncrossed stereopsis as reported in past research arose, in part, from effects related to occlusion.