Stochastic saliency-based search model for search asymmetry with uncertain targets

Whereas some models with mechanism coding task-related information, e.g. task-related saliency map, can explain why search asymmetry occurs in some visual search tasks where the target is preliminarily defined, existing models cannot clearly explain human behavior in singleton search tasks showing search asymmetry. This study shows that the saliency-based search model can explain search asymmetry in singleton search without assuming task-related saliency map if we introduce two new essential ideas. The first improvement is about a competitive mechanism between feature maps, and the other is the introduction of a stochastic winner takes all (WTA) network. According to the modified model introducing these two modifications, search asymmetry in singleton search tasks results from an asymmetry in probability of the attentional focus being directed to the target. When the saliency difference is large, then attentional focus is almost always directed to the target first. On the other hand, when the saliency difference is relatively small, then the probability of the target receiving attentional focus first becomes relatively smaller. The stochastic saliency-based search model could reproduce human behavior in a range of visual search tasks showing search asymmetry, without assuming task-related saliency map.