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Norma Graham

Publications and source records attributed to Norma Graham.

2 recordsLinked to original sources

Element-arrangement textures in multiple objective tasks.

In his long years of studying visual perception, Jacob Beck made many contributions. This article is a short review of one line of his research--that we shared in--and then a presentation of some results from on-going research down the same line. In the 1980s Beck and his colleagues introduced a new kind of visual stimulus: element-arrangement texture patterns. A series of studies with these patterns has shown that a model containing spatial-frequency and orientation-selective channels can explain many aspects of texture perception as long as two kinds of nonlinear processes are also included; the published studies are briefly summarized. The new results come from multiple objective tasks requiring the observer to make simple discriminations between second-order element-arrangement textures. Results with the objective tasks replicate previously published results using subjective ratings, and the use of the objective tasks allows us to explore several more fine-grained questions about complex (second-order) channels and normalization.

Contrast Sensitivity↗

Is there opponent-orientation coding in the second-order channels of pattern vision?

Is there opponency between orientation-selective processes in pattern perception, analogous to opponency between color mechanisms? Here we concentrate on possible opponency in second-order channels. We compare several possible second-order structures: SIGN-opponent-only channels in which there is no opponency between orientations (also called complex channels or filter-rectify-filter mechanisms); three structures we group under the name ORIENTATION-opponent; and finally BOTH-opponent channels which combine features of both SIGN-opponent-only and ORIENTATION-opponent channels but lead to predictions that are distinct from either of theirs. We measured observers' ability to segregate textures composed of checkerboard and striped arrangements of vertical and horizontal Gabor grating patches. The observers' performance was compared to model predictions from the alternative opponent structures. The experimental results are consistent with SIGN-opponent-only channels. The results rule out the ORIENTATION-opponent and BOTH-opponent structures. Further, when the models were expanded to include a contrast gain-control (inhibition among channels in a normalization network) the SIGN-opponent-only model was also able to explain a contrast-dependent effect we found, thus providing another piece of evidence that such normalization is an important process in human texture perception.

Adult↗