Orienting and focusing of visual attention are two processes strictly involved in reading. They were studied in a group of dyslexic children and normal readers. Shifting of attention by both peripheral and central visual cues was studied by means of the covert orienting paradigm. Focusing, consisting in the ability to control the size of the attentional focus, was investigated using simple reaction times in central vision. Results showed that dyslexics had a specific disability in the shifting of attention caused by a peripheral cue at short SOAs, and were also able to maintain attention focused for short periods of time only, presumably not long enough for efficient visual processing. Our results support the suggestion that visual selective attention deficits in disabled readers may be due to a specific difficulty in orienting and focusing.

Issues concerning selective attention provoke new questions about visual segmentation, and vice-versa. We illustrate this by describing our recent work on grouping under conditions of inattention, on change blindness for background events and the residual processing of undetected background changes, on modal versus amodal completion in visual search, and the differential effects of these two forms of completion on attentional processes, and on attentional modulation of lateral interactions thought to arise in early visual cortex. Many of these results indicate that segmentation processes substantially constrain attentional processes, but the reverse in¯uence is also apparent, suggesting an interactive architecture. We discuss how the`proto-objects' revealed by studies of segmentation and attention (i.e. the segmented perceptual units which constrain selectivity) may relate to other object-based notions in cognitive science, and we wrestle with their relation to phenomenal visual awareness. q

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Lateralised ERP responses were measured over posterior visual brain regions in response to visual search arrays that contained one colour singleton. In the localisation task, responses were determined by the visual hemifield where this singleton was presented. In the discrimination task, they were determined by the singletons' shape. While an N2pc component was elicited in an identical fashion in both tasks, a subsequent sustained contralateral negativity was consistently present at posterior sites in the discrimination task only. This dissociation demonstrates that these two activations reflect distinct visual processing stages. We suggest that while the N2pc reflects the ability of the visual system to both identify and localise a relevant stimulus in the scene, the late sustained activity reflects the subsequent in-depth analysis and identification of these stimuli. Keywordsvisual-spatial attention; visual cognition; visual working memory; attentional control; eventrelated brain potentials Visual attention selects relevant objects in the environment to enable their localisation and identification and to ensure that response selection is based on appropriate perceptual information. The idea that the attentional processing of visual stimuli consists of, at least partially, separable and sequential processes (such as spatial selection and stimulus identification) is central to many models of visual cognition (e.g., Treisman & Gelade, 1980;Treisman, 1996).The aim of the present study was to investigate whether the process of localising relevant items in the scene, as reflected by attentional orienting processes, and further detailed analyses of the selected items can be reflected by distinct electrophysiological responses. We recorded event-related brain potentials (ERPs) in two visual search tasks that were identical with respect to physical stimulus parameters, and only differed in the level of visual processing required to determine the correct response. We presented circular arrays of twelve coloured diamond shapes that had a corner cut off on the left or right side (see Figure