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

Abstract

We examined whether the processing of discontinuities involved in figure-ground segmentation, like line ends, can be modulated under selective attention conditions. Subjects decided whether a gap in collinear or parallel lines was located to the right or left. Two stimuli were displayed in immediate succession. When the gaps were on the same side, reaction times (RTs) for the second stimulus increased when collinear lines followed parallel lines, or the reverse, but only when the two stimuli shared the same orientation and location. The effect did not depend on the global form of the stimuli or on the relative orientation of the gaps. A frame drawn around collinear elements affected the results, suggesting a crucial role of the "amodal" orthogonal lines produced when line ends are aligned. Including several gaps in the first stimulus also eliminated RT variations. By contrast, RT variations remained stable across several experimental blocks and were significant for interstimulus intervals from 50 to 600 msec between the two stimuli. These results are interpreted in terms of a modulation of the processing of line ends or the production of amodal lines, arising when attention is selectively drawn to a gap.

Dissociation between perceptual processing and priming in long-term lorazepam users

“…# These are sometimes visible, like in the Ehrenstein illusion ( Figure 2, Gove et al, 1995 ;Lesher and Mingolla, 1993 ;von der Heydt and Peterhans, 1989 ;Westheimer and Li, 1996). In our stimuli, perpendicular lines are not consciously perceived, but are nevertheless produced (Giersch, 2001 ;Giersch and Fahle, 2002 ;Giersch and Caparos, 2005 ;Gurnsey et al, 1999 ;von der Heydt and Peterhans, 1989).…”

“…When the gap to be detected is between parallel elements, however, the two line terminations forming the gap produce a perpendicular line that is in exactly the same place as the gap and closes the stimulus (Figure 2b). We have suggested that the processing of line terminations is modulated in healthy volunteers (Giersch and Caparos, 2005 ;Giersch and Fahle, 2002), and that lorazepam affects this modulation (review in Giersch, 2001 ;Lorenceau et al, 2005), which explains why lorazepam-treated subjects separate elements even when they are collinear, at least when contour processing is modulated. Several studies have suggested that the effects of lorazepam on the processing of line terminations thus impairs the binding of the local elements composing the object (Giersch et al, 1997 ;Giersch and Lorenceau, 1999 ;Lorenceau et al, 2005).…”

“…For the sake of simplicity, we focus here on the conditions allowing a modulation of contour processing to be observed, i.e. when the two consecutive stimuli change in form (Giersch and Fahle, 2002 ;Giersch and Caparos, 2005). These are the conditions in which a deleterious effect of an acute dose of lorazepam has been observed (Giersch, 2001).…”

A Dorsal Visual Route Necessary for Global Form Perception: Evidence from Neuropsychological fMRI

“…The output of this integration process is then forwarded to higher-level regions responding to global pattern structure (e.g., the lateral occipital complex [LOC], more anterior temporal cortex). Consistent with this view, lesions to intermediate visual areas are associated with disorders in the organization of visual elements into recognizable whole patterns (Giersch, 2002;Milner et al, 1991;Riddoch & Humphreys, 1987).…”

Lack of flexibility in visual grouping in patients with schizophrenia.

“…We argue that local–global processing, that is, the classical distinction between the coding of details and global forms (Navon, 1977), is not enough to resolve such cases, because neither pair of individuals corresponds to either local information (one individual) or global information (the crowd). It does not suppress the risk of fragmentation that may occur when two objects that belong to two different groups must be considered as one (Giersch & Caparos, 2005; Giersch & Fahle, 2002). This question is all the more crucial because it can in fact occur quite often in everyday life, for instance, in cases where visual scenes are rich and complex.…”