Feature analysis and the role of similarity in preattentive vision

Abstract

Texture arrays of line elements at various orientations were used to study three phenomena of preattentive vision. Subjects were asked (1) to discriminate texture areas and to distinguish their form (experiments on texture segmentation); (2) to detect salient or vertical line elements (experiments on pop-out); and (3) to identify configurations of similar or dissimilar targets (experiments on grouping). Within the patterns, line orientation was systematically varied to distinguish the effect of differences between areas from the effect of similarity within areas. In all of the experiments, performance was found to depend on local orientation contrast at texture borders rather than on the analysis ofline orientation itself. Texture areas were correctly identified only when the orientation contrast at the border well exceeded the overall variation of line orientation in the pattern. Similarly, only target elements with high local orientation contrast were detected fast and "in parallel." Targets with an orientation contrast lower than background variation required serial search. Preattentive grouping was found to depend on saliency, as defined by local orientation contrast, but not on the similarity of line elements. In addition to local orientation contrast, which played an important role in all of the visual phenomena studied, influences from the alignment of line elements with the outline of a figure were also seen.Three spontaneous perceptual phenomena have been described as occurring in the visual inspection of line arrays with differently oriented elements: (1) The pattern may segregate into distinct areas, each of which appears to be separated from neighboring areas by a clearly visible (but physically nonexistent) texture border (texture segmentation; Beck, 1966bBeck, , 1972Beck, , 1982Julesz, 1975Julesz, , 1984Olson & Attneave, 1970). (2) Individual line elements at an orientation different from that of the rest of the pattern appear to be particularly salient and are instantaneously detected in search experiments (pop-out;Treisman, 1985Treisman, , 1986Treisman & Gormican, 1988). (3) Lines at similar orientations may be seen as grouping together, forming distinct ensembles of elements within the line pattern (grouping; Beck, 1966a Beck, , 1967. Although these phenomena have been discovered independently of each other, and although they have been quantitatively assessed in different ways, they share important properties. They can all be achieved by preattentive visionthat is, without detailed analysis of the pattern-and they all seem to recruit from the same set of visual features. In general, elements that do not segregate in texture segmentation tasks also do not pop out from each' other or provide perceptual grouping. Controversial reports, ac-I would like to thank Peter Ruhlender for a suggestion concerning Experiment 5 and Jacob Beck, Rick Gurnsey. Lester Krueger. Jeremy Wolfe. and an anonymous referee for helpful comments on an earlier version of the manuscript. I am grateful to all of the subjects ...

Pop-out from abrupt visual onsets

“…Pop-out paradigms are usually designed to study texture segmentation involving rapid pre-attentive processes that apply in parallel across the visual field (e.g. Nothdurft, 1991;1992), and performance in these paradigms has been related in detail to single unit neurophysiological studies of primary visual cortex (e.g. Kastner, Nothdurft & Pigarev, 1997, Nothdurft, 2002.…”

“…The task and stimuli used are therefore comparable to those used in several prior studies of pop-out (e.g. Nothdurft, 1992Nothdurft, , 2000Nothdurft, , 2002, in that they require the rapid detection of a contrasting element within a very large set of elements (about 160 in our experiments). Accurate detection under such conditions is assumed to predominantly reflect fast preattentive processes rather than post-attentive serial search processes.…”

“…Such elements are therefore said to 'pop-out' (Nothdurft 1991). Rapid detection within a large array of surrounding elements is evidence that this figure-ground segregation occurs preattentively (Bergen & Julesz, 1983;Nothdurft, 1992). As pop-out effects are strong and well established we designed our experiments to ask whether they apply specifically to the perception of a set of abrupt onsets containing one element that contrasts with all the other new elements.…”

Evidence against global attention filters selective for absolute bar-orientation in human vision

“…A target bar of a given orientation pops out from a field of distractor bars of some other fixed orientation provided the difference in orientation between target and distractor bars is large enough (Beck & Ambler, 1973;Foster & Ward, 1991a;, 1998Nothdurft, 1991Nothdurft, , 1992Nothdurft, , 1993Nothdurft, , 1994Sagi & Julesz, 1985;Treisman, 1985;Treisman & Souther, 1985;Wolfe et al, 1992). This frequently replicated result might be taken to suggest that human vision possesses a number (perhaps a continuum) of mechanisms selective for different orientations.…”

“…Other research, however, both psychophysical (Nothdurft, 1991(Nothdurft, , 1992(Nothdurft, , 1993(Nothdurft, ,1994Koene & Li, 2007;Sagi & Julesz, 1985) and neurophysiological (Kastner, Nothdurft & Pigarev, 1999;Nothdurft, Gallant & Van Essen, 1999, 2000Schofield & Foster, 1995;Van Essen et al, 1989) suggests that human vision possesses at least one mechanism sensitive to Borientation contrast^(as opposed to absolute orientation). Such mechanisms are hypothesized to respond not to bars of a specific, absolute orientation but rather to visual input patterns in which the predominant direction of bar orientation undergoes an abrupt change.…”