Attention Mechanisms in Visual Search—An fMRI Study

Abstract

The human visual system is usually confronted with many different objects at a time, with only some of them reaching consciousness. Reaction-time studies have revealed two different strategies by which objects are selected for further processing: an automatic, efficient search process, and a conscious, so-called inefficient search [Treisman, A. (1991). Search, similarity, and integration of features between and within dimensions. Journal of Experimental Psychology: Human Perception and Performance, 17, 652--676; Treisman, A., & Gelade, G. (1980). A feature integration theory of attention. Cognitive Psychology, 12, 97--136; Wolfe, J. M. (1996). Visual search. In H. Pashler (Ed.), Attention. London: University College London Press]. Two different theories have been proposed to account for these search processes. Parallel theories presume that both types of search are treated by a single mechanism that is modulated by attentional and computational demands. Serial theories, in contrast, propose that parallel processing may underlie efficient search, but inefficient searching requires an additional serial mechanism, an attentional "spotlight" (Treisman, A., 1991) that successively shifts attention to different locations in the visual field. Using functional magnetic resonance imaging (fMRI), we show that the cerebral networks involved in efficient and inefficient search overlap almost completely. Only the superior frontal region, known to be involved in working memory [Courtney, S. M., Petit, L., Maisog, J. M., Ungerleider, L. G., & Haxby, J. V. (1998). An area specialized for spatial working memory in human frontal cortex. Science, 279, 1347--1351], and distinct from the frontal eye fields, that control spatial shifts of attention, was specifically involved in inefficient search. Activity modulations correlated with subjects' behavior best in the extrastriate cortical areas, where the amount of activity depended on the number of distracting elements in the display. Such a correlation was not observed in the parietal and frontal regions, usually assumed as being involved in spatial attention processing. These results can be interpreted in two ways: the most likely is that visual search does not require serial processing, otherwise we must assume the existence of a serial searchlight that operates in the extrastriate cortex but differs from the visuospatial shifts of attention involving the parietal and frontal regions.

Visual search in Alzheimer’s disease: a deficiency in processing conjunctions of features

“…AD is associated with multi-focal pathological changes affecting many areas of visual processing [5,22,25] which may therefore affect many more aspects of visual function in addition to those related to the attention-related aspects of visual search. For example, recent fMRI data [24] do not clearly point to a dissociation between conjunction and single-feature search in visual cortex but do reveal differential activity in relation to the solution of the "binding problem". Thus, the differences found in our study may relate to aspects of vision not particularly related to visual search, but rather to "binding" difficulties or a failure of inhibition of responses to heterogeneous distractors.…”

A Study of Temporal Aspect of Posterior Parietal Cortex in Visual Search Using Transcranial Magnetic Stimulation

“…Both neuroimaging in humans (30) and single-unit recordings in monkeys (31) have revealed that the PPC subregions controlling spatial selection are also implicated in the selection of nonspatial features, suggesting that the involvement of the PPC in the visual search may not be binding-specific but rather reflect more general attention mechanisms. Furthermore, Leonards et al (32) and Donner et al (33) also reported PPC activations during the feature search task. Therefore, it was considered that the PPC plays a key role in the spatial perception and attention during visual search task.…”

Contrôle du mouvement du regard (2)

“…D'une façon générale, cette région occupe probablement une place importante dans la supervision des actions à exécuter. Une autre région, juste en avant du COF dorsomédian, dans le sillon frontal supérieur, intervient dans la mémoire spatiale à court terme [14,15].…”

“…Ainsi, S.A. Brandt et al [19] L'imagerie fonctionnelle a permis d'explorer l'activité corticale mise en jeu lorsqu'on demande à des sujets de reproduire de mémoire une séquence qu'ils viennent d'effectuer de façon visuellement guidée [20][21][22][23]. En plus du réseau cortical impliqué dans le contrôle des saccades simples, les séquences de saccades activent un circuit composé principalement du précuneus, d'une région située dans le sillon intrapariétal, d'une région antérieure au COS et d'une région antérieure au COF, située dans le sillon frontal supérieur, qui correspond à un foyer déjà impliqué dans la mémoire spatiale à court terme (voir plus haut) [14] ou dans l'exploration spatiale [15]. Ces régions seraient donc activées spécifiquement dans l'exécution volontaire de séquences de saccades mémorisées, mais pas dans l'exécution de saccades simples (Figure 3).…”