Electrophysiological evidence for parallel and serial processing during visual search

Abstract

Event-related potentials were recorded from young adults during a visual search task in order to evaluate parallel and serial models of visual processing in the context of Treisman's feature integration theory. Parallel and serial search strategies were produced by the use offeature-present and feature-absent targets, respectively. In the feature-absent condition, the slopes of the functions relating reaction time and latency of the P3 component to set size were essentially identical, indicating that the longer reaction times observed for larger set sizes can be accounted for solely by changes in stimulus identification and classification time, rather than changes in postperceptual processing stages. In addition, the amplitude of the P3 wave on target-present trials in this condition increased with set size and was greater when the preceding trial contained a target, whereas P3 activity was minimal on target-absent trials. These effects are consistent with the serial self-terminating search model and appear to contradict parallel processing accounts of attention-demanding visual search performance, at least for a subset of search paradigms. Differences in ERP scalp distributions further suggested that different physiological processes are utilized for the detection of feature presence and absence.

Effect of Methylphenidate on Attention in Children with Attention Deficit Hyperactivity Disorder (ADHD) ERP Evidence

“…As we analyzed components only when a correct response was made on a hit trial, only these processes will be considered. The P2 component is thought to reflect feature detection (Luck and Hillyard, 1994) and would occur in the present task after the second stimulus is detected. The N2 component reflects focused at- tention to stimulus features (Breton et al 1988).…”

“…The cognitive processes linked with each of these waves and their underlying, cortical sources have not been definitively identified; however, increased specificity for ERP components have been determined showing that components can reflect cognitive processes at specific neuroanatomical locations (e.g., Nobre et al 1994). The following are the cognitive processes associated with attention-related ERP components: N1 is thought to reflect the shifting of attention to a location and is observed mostly in posterior (i.e., parietal) structures (Mangun et al 1993;Novak et al 1995); P2 reflects feature detection and is observed centrally and frontally (Luck and Hillyard 1994); N2 reflects target identification when it is observed at anterior locations (Breton et al 1988); and P3, the most commonly studied component, is thought to reflect updating working memory and post decisional processes. The P3 component is largest over parietal and central regions (Picton 1992).…”

Electrophysiological Evidence of Atypical Spatial Attention in Those with a High Level of Self-reported Autistic Traits

“…This was achieved by presenting stimulus arrays of two to four items from which the relevant target must be identified and processed while the distracting stimuli also present should be ignored. This task generates the N2pc ERP component, which is a posterior component in the N2 time-range, recorded from electrodes over temporal/parietal areas (~200 to 300 ms post stimulus onset, Luck & Hillyard, 1990;1994a;1994b) The N2pc represents the difference between the signal recorded from electrodes that are either contralateral or ipsilateral to a target (Woodman & Luck, 1999). For example, when presented with a visual search display, amplitude is larger at electrodes that are contralateral to the target than electrodes that are ipsilateral to the target., The source of the N2pc has been localised to the ventral occipital cortex (Hopf et al, 2000), and the cognitive process reflected by the N2pc is the deployment of covert attention in order to select a target in space (Eimer, 1996;Kiss, Van Velzen & Eimer., 2008).…”

Are attentional dwell times inconsistent with serial visual search?

“…Therefore, this pattern cannot be taken as strictly diagnostic of serial processing. Other methods have been developed to distinguish between serial and limitedcapacity parallel processing, but no consensus has been reached concerning the nature of second-stage processing (Egeth & Dagenbach, 1991;Luck & Hillyard, 1990;Townsend, 1990). …”