A coincidence detector neural network model of selective attention

A coincidence detector neural network model of selective attention Kleanthis Neokleous 1 (kleneokl@cs.ucy.ac.cy) Maria Koushiou 2 (maria_koushiou@yahoo.com) Marios N. Avraamides 2 (mariosav@ucy.ac.cy) Christos Schizas 1 (schizas@ucy.ac.cy) Department of Computer Science, 2 Department of Psychology University of Cyprus P.O Box 20537, Nicosia, Cyprus Abstract A computational model of selective attention is implemented to account for findings from an experiment on selective attention that was conducted. The model successfully reproduces the latency data of human participants by relying on the interaction between a bottom-up saliency map and the top-down influences from spatial and semantic goals. The model offers a biologically-plausible way of operationalizing perceptual load and provides insights about the possible brain mechanisms that underlie related empirical findings. Keywords: selective attention, perceptual load, coincidence detector, neural synchronization. Introduction At every moment of conscious life a person experiences a plethora of information that is present in the environment. As processing all available stimulation would represent a daunting task for the perceptual apparatus, a person selects only a subset of information from what is available and discards the rest. The process of focusing mental resources on part of the visual stimulation to allow further processing while ignoring everything else is commonly referred to as selective attention. Over the years a theoretical debate arose over the locus of selection in the information processing stream. On one hand, early-selection theories of attention (Broadbent, 1958) had posited that selection occurs at an early stage of processing based on the physical characteristics of the stimuli (e.g., intensity, tone). According to these theories, unattended stimuli are discarded from further processing with only some of their physical characteristics being registered. These stimuli are therefore discarded prior to any semantic analysis. On the other hand, late-selection theories (Deutsch & Deutsch, 1963) have placed selection at a later processing stage. These theories have argued that all stimuli enter short-term memory and are thus processed semantically. Those stimuli that are deemed as more important or relevant to the task are then selected and guide response execution. More recently, Lavie (1995) provided results showing that selection may be early or late depending on task characteristics. In one of Lavie’s studies participants were asked to determine whether a presented stimulus was the letter x or the letter z. In one condition, termed the high- load, the letter was flanked by 5 other letters. In another condition, termed the low-load condition, the target was presented accompanied by no flanking letters. In both conditions a distractor letter was presented nearby the target. In a subset of trials the distractor was incompatible to the target designating the alternative response (i.e., if the target was x the distractor was z and vice-versa). In other trials, the distractor was a neutral letter. Results revealed that the interference exerted by the incompatible distractor, evidenced as increased latency for identifying the target, was greater in the low than the high load condition. Lavie accounted for these findings by arguing that in the high-load condition all attentional resources are consumed by the main task leaving no spare resources to process the distractor; that is, the distractor is discarded at an early stage of processing. In contrast, in the low-load condition the task does not exhaust all available resources leaving spare resources to process the distractor. In this case, the distractor is discarded at a later-stage. Although the Perceptual Load theory offers an appealing account for how selection of information can occur either early or late, it has been recently criticized and challenged. For example, Johnson, McGratth, and McNeil (2002) have shown that an endogenous cue priming the location of the target (i.e., a central arrow presented prior to the target display) eliminates any distractor interference in the low- load condition. As the presentation of a cue does not alter the amount of spare resources, this result is problematic for at least a strong version of the Perceptual Load theory. Furthermore, Elitti, Wallace, and Fox (2005) provided evidence that the critical variable might be the saliency of distractors and not perceptual load per se. In their experiments that manipulated the onsets and offsets of targets and distractors, Elitti et al. showed that interference can be present with high-load provided that the distractor is