Modulations of the processing of line discontinuities under selective attention conditions?

Giersch, Anne; Fahle, Manfred · 2002 · Crossref

DOI: 10.3758/bf03194558

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Summary

This study investigates whether the processing of line discontinuities, such as gaps and line ends involved in figure–ground segmentation, can be modulated by selective attention. The authors address the question of whether top-down attentional processes can influence early visual coding of primitives, specifically testing if the detection of a gap in one configuration affects the processing of a gap in another. The research is motivated by evidence that visual primitives are more plastic than previously believed and that feedback connections from higher cortical areas can modulate early processing in V1 and V2. The researchers employed a modified short-term priming task across four experiments. Subjects viewed two stimuli in immediate succession and decided whether a gap in collinear or parallel line segments was located to the right or left. Experiment 1 established that reaction times (RTs) for the second stimulus increased when the gap configuration changed (e.g., from collinear to parallel) but remained on the same side, whereas RTs decreased if the configuration was identical. Experiments 2, 3, and 4 controlled for potential confounds, including the global form of the stimuli, the relative orientation of the gaps, and the spatial location of the discontinuities. Additional manipulations included drawing frames around elements and varying the number of gaps in the first stimulus. The results demonstrated that the RT disadvantage for same-side gaps with differing configurations was robust and specific. It persisted even when the global form of the stimuli was made similar (Experiment 2) and was not dependent on the relative orientation of the gaps (Experiment 3). The effect was strictly location-specific, occurring only when stimuli shared the same orientation and screen location (Experiment 4). Furthermore, the modulation remained stable across experimental blocks and for interstimulus intervals ranging from 50 to 600 msec. However, the effect was eliminated when a frame was drawn around collinear elements or when multiple gaps were included in the first stimulus, suggesting a crucial role for "amodal" orthogonal lines produced by aligned line ends. The authors conclude that the processing of line ends and the production of amodal lines are modulated when attention is selectively drawn to a gap. The findings suggest that detecting a gap in a specific configuration activates mechanisms that enhance line-end signals, which can be deleterious for detecting gaps in configurations where such signals are inconsistent with the presence of a true gap. This provides evidence for top-down influences on early visual processing, indicating that attentional control can modulate the coding of image primitives to facilitate figure–ground segmentation.

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