Attentional selection and identification of visual objects are reflected by distinct electrophysiological responses

Abstract

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

EPS Mid-Career Award 2014

“…In the absence of such recurrent feedback loops, any spatially specific enhancement of object processing that is triggered in visual cortex during the initial object selection stage is assumed to remain transient and fade rapidly, as was observed in the localisation task of our ERP study (Mazza et al, 2007). Regions in the intraparietal sulcus that are sensitive to working memory load and individual capacity limits (e.g., Todd & Marois, 2004;Xu & Chun, 2006) may play a central role in sustaining visual working memory representations of target objects in visual cortex when these objects have to be recognized.…”

“…But are there situations where objects are selected without subsequently being encoded in working memory? Electrophysiological evidence for selection without memorybased recognition was found in a visual search study from our lab (Mazza, Turatto, Umiltà, & Eimer, 2007) where observers had to select a colour singleton target among uniform distractor objects in two different task conditions. In a localisation task, they simply had to report whether the target appeared in the left or right visual field.…”

The gradual emergence of spatially selective target processing in visual search: From feature-specific to object-based attentional control.

“…Working memory maintenance is known to be associated with sustained negative ERP components at contralateral posterior electrodes (e.g., Vogel & Machizawa, 2004: Mazza et al, 2007Jolicoeur, Brisson, & Robitaille, 2008).…”

The neural basis of attentional control in visual search

“…The N2pc component reflects target selection, and a later sustained posterior contralateral negativity is elicited during the subsequent object identification stage [56,57].…”

“…In contrast, the subsequent sustained posterior contralateral negativity (SPCN) that is generated during the identification stage when selected objects are maintained in working memory [58] was reliably triggered only in the shape discrimination task, demonstrating that selection and identification are separable stages of visual search. Data from [56], reproduced in a different format. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 …”