Temporal Processing of Saccade Targets in Parietal Cortex Area LIP During Visual Search

Abstract

Thomas NW, Paré M. Temporal processing of saccade targets in parietal cortex area LIP during visual search. J Neurophysiol 97: [942][943][944][945][946][947] 2007. First published November 1, 2006; doi:10.1152/jn.00413.2006. We studied whether the lateral intraparietal (LIP) area-a subdivision of parietal cortex anatomically interposed between visual cortical areas and saccade executive centers-contains neurons with activity patterns sufficient to contribute to the active process of selecting saccade targets in visual search. Visually responsive neurons were recorded while monkeys searched for a color-different target presented concurrently with seven distractors evenly distributed in a circular search array. We found that LIP neurons initially responded indiscriminately to the presentation of a visual stimulus in their response fields, regardless of its feature and identity. Their activation nevertheless evolved to signal the search target before saccade initiation: an ideal observer could reliably discriminate the target from the individual activation of 60% of neurons, on average, 138 ms after stimulus presentation and 26 ms before saccade initiation. Importantly, the timing of LIP neuronal discrimination varied proportionally with reaction times. These findings suggest that LIP activity reflects the selection of both the search target and the targeting saccade during active visual search.

Functional Heterogeneity of Macaque Lateral Intraparietal Neurons

“…Our single-and multiple-distractor tasks were effectively pop-out tasks (targets and distractors differed in color) and therefore similar to the pop-out task used in Buschman and Miller (2007). As a population, LIP neurons detected the location of the target as early as 52 ms after stimulus onset, which is similar to the 50 ms selectivity latency of the fastest neurons reported by Buschman and Miller (2007) but much faster compared with other LIP studies (Thomas and Paré, 2007;Ipata et al, 2009), and considerably faster than the oddballdetection latencies reported for FEF (130 -140 ms) (Schall et al, 2007). Importantly, these short selectivity latencies cannot be explained by the mere difference in visual stimulation in the RF (target and distractor vs distractor in RF), as we obtained equally short latencies in the single-distractor saccade task (target vs distractor in RF).…”

Deficits in reach target selection during inactivation of the midbrain superior colliculus

“…For example, activity related to eye-movement target selection has been identified in the superior colliculus (SC) (7,(11)(12)(13)(14)(15)(16)(17), frontal eye field (18)(19)(20), lateral intraparietal area (10,(21)(22)(23), and supplementary eye fields (24), all areas in which signals related to eye movement execution are seen and in which electrical microstimulation and/or temporary inactivation affects the execution of eye movements (25)(26)(27)(28)(29)(30)(31). For reaching movements, target selection activity has been observed in the dorsal premotor area (32)(33)(34), a region from which reaches can be electrically elicited (35), as well as in the parietal reach region (36,37), which exhibits reach-related planning and execution signals (38,39).…”

Brain bases of the automaticity via visual search task

“…Then, we also found changes in the inferior occipital gyrus that could be linked to the PPC. On visual search tasks designed to investigate the priority map function, it has been observed that occipital gyrus neurons do not respond to task demands as the PPC does; the PPC responds more to targets than the occipital gyrus (Ipata et al, 2006;Buschman and Miller, 2007;Thomas and Paré, 2007;Mirpour et al, 2009). The decreased activation in occipital gyrus areas could be explained by repetition suppression mechanisms .…”

“…Supporting this hypothesis, researchers have been observing that maps in early visual areas do not respond to task demands like the PPC does. For example, during visual search tasks, enhanced PPC response was observed more for targets than for distractors (Ipata et al, 2006;Buschman and Miller, 2007;Thomas and Paré, 2007;Mirpour, Arcizet, Ong and Bisley, 2009). It seems that during visual search tasks, the focus of attention is guided through the visual scene using the priority map, where the targets are highlighted and the distractors are suppressed .…”

“…Supporting this hypothesis, researchers have been observing that maps in early visual areas do not respond to task demands like the PPC does. For example, during visual search tasks, enhanced PPC response was observed more for targets than for distractors (Ipata et al, 2006;Buschman and Miller, 2007;Thomas and Paré, 2007;Mirpour, Arcizet, Ong and Bisley, 2009 seems that during visual search tasks, the focus of attention is guided through the visual scene using the priority map, where the targets are highlighted and the distractors are suppressed . Inherited from bottom-up saliency models (Itti and Koch, 2001), it seems that the PPC also engages inhibition of return to suppress already visited locations in the space, making it possible for the visual attention system to progress in the search by dismissing potential objects that eventually do not match the target (Mirpour et al, 2009).…”