Discrimination between similar stimuli is enhanced more by intermixed pre-exposure than by blocked pre-exposure to those stimuli. The salience modulation account of this intermixed-blocked effect proposes that the unique elements of intermixed stimuli are more salient than those of blocked stimuli. The inhibition account proposes that inhibitory links between the unique elements of intermixed stimuli enhance discrimination. The current thesis evaluated the two accounts in their ability to explain this effect in humans. In Experiments 1 and 2, categorisation and same-different judgements were more accurate for intermixed than for blocked stimuli. This indicates that intermixed pre-exposure decreases generalisation and increases discriminability more than does blocked pre-exposure. In Experiments 3 ?? 5, same-different judgements were more accurate when at least one of the two stimuli was intermixed. This enhanced discrimination was not confined to two stimuli that had been directly intermixed. These results are better explained by salience modulation than by inhibition. Experiments 6 ?? 8 employed dot probe tasks, in which a grid stimulus was followed immediately by a probe. Neither intermixed nor blocked stimuli showed facilitated reaction times when the probe appeared in the location of the unique element. In Experiments 9 ?? 11 participants learned to categorise the intermixed unique elements more successfully than the blocked unique elements, but only when the unique elements were presented on a novel background during categorisation. Experiments 6 ?? 11 provide weak evidence that the intermixed unique elements are more salient than their blocked counterparts. In Experiment 12, participants were presented with the shape and location of a given unique element, and were required to select the correct colour. Performance was more accurate for intermixed than for blocked unique elements. In Experiment 13, participants learned to categorise intermixed, blocked and novel unique elements. Performance was better for intermixed than for blocked and novel unique elements, which did not differ. None of the proposed mechanisms for salience modulation anticipate these results. The intermixed-blocked effect in human perceptual learning is better explained by salience modulation than by inhibition. However, the salience modulation accounts that have been proposed received little support. An alternative account of salience modulation is considered.

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The mamalian visual system contains a limited number of receptors, which project to a limited number of cells in the visual cortex. This projection provides a point-to-point representation of the retinal stimulation onto the visual cortex. Data reported by Marshall and Talbot (1942) suggest that contours in the environment are represented on the visual cortex by a process involving the summation of neural activity around the area receiving the retinal projection. Such anatomical and physiological evidence suggests a simple mechanism by which forms are perceived; the perception of form should correspond to retinal stimulation by form. [...]

Pattern vision in the rat bas been most effectively studied by a jumping method devised by Lashley (1930). This procedure requires the rat to jump at one of two cards bearing the patterns to be discriminated. On the basis of Laehley’s extensive anatomical and behavioural studies it has been assumed that the cards fall within the rat’s binocular field of vision and, consequently, that they are seen as a whole at the time when the visual patterns begin to influence behaviour during discrimination learning. Ehrenfreund (1948), however, thought that the rat’s effective field, in the Lashley jumping apparatus, might be limited to the lower margin of the cards, and has demonstrated this experimentally in certain conditions of training. Since Ehrenfreund’s data have been interpreted as bearing on the current continuity-noncontinuity controversy concerning the nature of learning, his experiment is of general importance. Ehrenfreund trained his rats on a modified Lashley jumping apparatus to discriminate between an upright and an inverted triangle in two differing experimental situations. In one condition, the triangles were raised eight centimetres above the bottom margin of the cards. The platform from which the rats jumped, as in the usual procedure, remained level with the platform on which they found food. In the second, the platform was also raised, so that the rats were jumping at the centre of the cards where the triangles were now located. [...]

This research is concerned with texture: a source of visual information, that has motivated a huge amount of psychophysical and computational research. This thesis questions how useful the accepted view of texture perception is. From a theoretical point of view, work to date has largely avoided two critical aspects of a computational theory of texture perception. Firstly, what is texture? Secondly, what is an appropriate representation for texture? This thesis argues that a task dependent definition of texture is necessary, and proposes a multi-local, statistical scheme for representing texture orientation. Human performance on a series of psychophysical orientation discrimination tasks are compared to specific predictions from the scheme. The first set of experiments investigate observers' ability to directly derive statistical estimates from texture. An analogy is reported between the way texture statistics are derived, and the visual processing of spatio-luminance features. The second set of experiments are concerned with the way texture elements are extracted from images (an example of the generic grouping problem in vision). The use of highly constrained experimental tasks, typically texture orientation discriminations, allows for the formulation of simple statistical criteria for setting critical parameters of the model (such as the spatial scale of analysis). It is shown that schemes based on isotropic filtering and symbolic matching do not suffice for performing this grouping, but that the scheme proposed, base on oriented mechanisms, does. Taken together these results suggest a view of visual texture processing, not as a disparate collection of processes, but as a general strategy for deriving statistical representations of images common to a range of visual tasks.

Discrimination between similar stimuli is enhanced more by intermixed pre-exposure than by blocked pre-exposure to those stimuli. The salience modulation account of this intermixed-blocked effect proposes that the unique elements of intermixed stimuli are more salient than those of blocked stimuli. The inhibition account proposes that inhibitory links between the unique elements of intermixed stimuli enhance discrimination. The current thesis evaluated the two accounts in their ability to explain this effect in humans. In Experiments 1 and 2, categorisation and same-different judgements were more accurate for intermixed than for blocked stimuli. This indicates that intermixed pre-exposure decreases generalisation and increases discriminability more than does blocked pre-exposure. In Experiments 3 ?? 5, same-different judgements were more accurate when at least one of the two stimuli was intermixed. This enhanced discrimination was not confined to two stimuli that had been directly intermixed. These results are better explained by salience modulation than by inhibition. Experiments 6 ?? 8 employed dot probe tasks, in which a grid stimulus was followed immediately by a probe. Neither intermixed nor blocked stimuli showed facilitated reaction times when the probe appeared in the location of the unique element. In Experiments 9 ?? 11 participants learned to categorise the intermixed unique elements more successfully than the blocked unique elements, but only when the unique elements were presented on a novel background during categorisation. Experiments 6 ?? 11 provide weak evidence that the intermixed unique elements are more salient than their blocked counterparts. In Experiment 12, participants were presented with the shape and location of a given unique element, and were required to select the correct colour. Performance was more accurate for intermixed than for blocked unique elements. In Experiment 13, participants learned to categorise intermixed, blocked and novel unique elements. Performance was better for intermixed than for blocked and novel unique elements, which did not differ. None of the proposed mechanisms for salience modulation anticipate these results. The intermixed-blocked effect in human perceptual learning is better explained by salience modulation than by inhibition. However, the salience modulation accounts that have been proposed received little support. An alternative account of salience modulation is considered.

Thesis(M.S.)--Auburn University, 2005. / Abstract. Vita. Refer also to: Wheeler, S. A. (2003). Measuring change blindness in specific phobia. Master's Thesis, Auburn University, 2004. Includes bibliographic references.

Thesis (PhD) - Faculty of Life and Social Sciences, Swinburne University of Technology, 2006. / Submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy, Faculty of Life and Social Sciences, Swinburne University of Technology - 2006. Typescript. "March 2006". Includes bibliographical references (p. 153-173).