Postadaptation orientation discrimination

Abstract

An orientational difference of only 0.3-0.5 deg can be discriminated between two gratings or two lines, although psychophysical channels and cortical cells both have comparatively broad orientation bandwidths of 10-25 deg. One proposed explanation for the fineness of orientation discrimination is that, while detection is determined by the most excited orientation-tuned neural elements, superthreshold orientation discrimination is determined by difference signals between these elements [Westheimer et al., J. Opt. Soc. Am. 66, 332 (1976)]. This implies that, if stimulus orientation is changed slightly, the most important elements for discriminating this change will be those whose relative activity changes most, even though the excitation of these elements may be comparatively weak. In accord with this prediction, we found that adapting to a high-contrast grating degraded discrimination for test gratings inclined at about 10-20 deg to the adapting grating while having little effect on the detection of these inclined gratings. For test gratings parallel to the adapting grating, discrimination was improved, but detection was degraded. Either an opponent-process or a line-element model can account for these effects of adaptation. An opponent model can also explain our findings that subjects do not confound orientation change with contrast change and that suprathreshold orientation discrimination is almost independent of contrast, varying by only +/- 10% from about 3 to about 25 times contrast threshold. A discrimination model must incorporate reliable storage of spatial frequency, because discrimination was not affected by increasing the interval between grating presentations from 1 to 10 sec.(ABSTRACT TRUNCATED AT 250 WORDS)

Moving towards solutions to some enduring controversies in visual search

“…With attention, we can easily discriminate between a vertical (0 deg) line and one tilted a degree or two to either side. Early cortical cells possess the information to perform these discriminations [17].…”

Do perceptual biases emerge early or late in visual processing? Decision-biases in motion perception

“…A model that re-weights sensory information away from the reference direction could quantitatively account for these biases. The weighting function in this model captures the shape of a mechanism tuned optimally for the fine-discrimination task [7,8], suggesting the re-weighting of information during the fine discrimination task as a potential cause for the observed perceptual biases. However, the biases in the reported motion directions could also have occurred later in the trial [5].…”

“…The authors accounted for these biases by implementing a model that reweights sensory information away from reference direction. In particular, the shape of the weighting function allows an optimization of the fine-discrimination task (see [7,8]). Jazayeri & Movshon [6], therefore, interpret these results as a re-weighting of sensory information during discrimination, which later in the task sequence emerges as a bias in the estimated percept.…”

Multiple groups of orientation–selective visual mechanisms underlying rapid orientated–line detection

“…Notice that detection is best at (or near to) the maximum of one mechanism's response, not where it is changing most rapidly, as in classical orientation acuity (cf. Regan & Beverley 1985). This scheme, proposed in Foster & Ward (1991) to explain the vertical-oblique asymmetry in line-element search (Treisman & Souther 1985), can be regarded as an example of a more general scheme proposed by Treisman & Gormican (1988) in which an oblique (or tilted) line element is coded as a vertical line element with an additional feature marking the nature of the deviation.…”