The impending demise of the item in visual search

Abstract

The way the cognitive system scans the visual environment for relevant information - visual search in short - has been a long-standing central topic in vision science. From its inception as a research topic, and despite a number of promising alternative perspectives, the study of visual search has been governed by the assumption that a search proceeds on the basis of individual items (whether processed in parallel or not). This has led to the additional assumptions that shallow search slopes (at most a few tens of milliseconds per item for target-present trials) are most informative about the underlying process, and that eye movements are an epiphenomenon that can be safely ignored. We argue that the evidence now overwhelmingly favours an approach that takes fixations, not individual items, as its central unit. Within fixations, items are processed in parallel, and the functional field of view determines how many fixations are needed. In this type of theoretical framework, there is a direct connection between target discrimination difficulty, fixations, and reaction time (RT) measures. It therefore promises a more fundamental understanding of visual search by offering a unified account of both eye movement and manual response behaviour across the entire range of observed search efficiency, and provides new directions for research. A high-level conceptual simulation with just one free and four fixed parameters shows the viability of this approach.

Distinct perceptual rhythms for feature and conjunction searches

“…However, these measures can be subject to multiple interpretations, because both the parallel and sequential models of attention predict that with more stimuli, reaction time increases and accuracy decreases (e.g., Buetti et al, 2016; Kristjánsson, 2015; McElree & Carrasco, 1999). Thus, other explanations have provided alternate interpretations of those search slopes characteristic of conjunction and feature searches (e.g., Cameron et al, 2004; Eckstein, 1998; Eckstein et al, 2000; Hulleman & Olivers, 2015; Kristjánsson, 2015; McElree & Carrasco, 1999; Verghese, 2001). Recently, Buetti et al (2016) have also challenged the original, strict parallel view of feature-search tasks and proposed that whereas all items in the search display start to be processed simultaneously, parallel search tends—because of the stochastic nature of processing—to produce logarithmic functions of reaction time with large set size 1 .…”

Target objects defined by a conjunction of colour and shape can be selected independently and in parallel

“…Because these distractors all have the potential to elicit feature-based attentional processing biases, adding more of 28 them to the same display will reduce the net attentional bias towards the target, and therefore make target-distractor discriminations more difficult. According to a recent suggestion by Hulleman & Olivers (2017), the difficulty of these discriminations determines the size of the functional viewing field (FVF) -the area within which attentional selection processes operate in parallel during any given fixation period. When conjunction search becomes more difficult because more partially matching distractors are added, the size of each FVF decreases, resulting in more eye movements and longer search times.…”

Search performance is better predicted by tileability than presence of a unique basic feature

“…FIT has explained a number of classic search phenomena, though a number of researchers have also pointed out issues both regarding FIT's ability to predict search results, and regarding the notion that only maps of basic features are available in preattentive vision. (e.g., Carrasco, Evert, Chang, & Katz, 1995; Carrasco, McLean, Katz, & Frieder, 1998; Carrasco & Yeshurun, 1998; Vlaskamp, Over, & Hooge, 2005; Wertheim, Hooge, Krikke, & Johnson, 2006; Reddy & VanRullen, 2007; Rosenholtz et al, 2012a; Hulleman & Olivers, 2015). …”