Right away: A late, right-lateralized category effect complements an early, left-lateralized category effect in visual search

Abstract

According to the Sapir-Whorf hypothesis, learned semantic categories can influence early perceptual processes. A central finding in support of this view is the lateralized category effect-namely, the finding that categorically different colors (e.g., blue and green hues) can be discriminated faster than colors within the same color category (e.g., different hues of green), especially when they are presented in the right visual field. Because the right visual field projects to the left hemisphere, this finding has been popularly couched in terms of the left-lateralization of language. However, other studies have reported bilateral category effects, which has led some researchers to question the linguistic origins of the effect. Here we examined the time course of lateralized and bilateral category effects in the classical visual search paradigm by means of eyetracking and RT distribution analyses. Our results show a bilateral category effect in the manual responses, which is combined of an early, left-lateralized category effect and a later, right-lateralized category effect. The newly discovered late, right-lateralized category effect occurred only when observers had difficulty locating the target, indicating a specialization of the right hemisphere to find categorically different targets after an initial error. The finding that early and late stages of visual search show different lateralized category effects can explain a wide range of previously discrepant findings.

No matter how: Top-down effects of verbal and semantic category knowledge on early visual perception

“…In RTs, there was no interaction of category and visual field, suggesting that the visual discrimination benefit was not stronger in (or exclusive to) targets in the RVF, in contrast with some previous findings (Drivonikou et al, 2007;Franklin et al, 2008;Gilbert, et al 2006;Roberson, Pak, & Hanley, 2008;Zhou et al, 2010) but in line with others (Witzel & Gegenfurtner, 2011, 2015, 2016. Roberson et al (2008) found lateralization of CP to the RVF only in fast responders (Constable & Becker, 2017). However, Bfastr eactions in previous studies were still relatively slow compared with the present study, suggesting that the visual search task used here was generally easier and more susceptible to bottom-up visual pop-out, and the average category-advantage was small compared to other studies.…”

“…Furthermore, CP is possible as soon as we acquire linguistic or semantic knowledge that allows forming conceptual stimulus categories. Whether this is also reflected in behavioral measures, such as RTs depends, in our opinion, on task difficulty (Constable & Becker, 2017;Regier & Xu, 2017). In line with a hierarchical predictive processing account of perception, linguistic category information may inform perceptual predictions and directly enhance perception (Clark, 2013;Friston, 2009;Lupyan & Clark, 2015), especially in difficult tasks with high perceptual uncertainty (Regier & Xu, 2017).…”

“…Given evidence that CP effects may differ between fast and slow responses (Constable & Becker, 2017;Witzel & Gegenfurtner, 2016), we tested whether the CP effect was distributed evenly across slow and fast RTs by splitting mean RTs into quartiles according to each individual participant's distribution of RTs (Fig. 2).…”

“…Thus, occurrence and lateralization of the behavioral CP effect appear to be task-dependent (Regier & Xu, 2017). We assume that visual discrimination needs to be difficult enough for categorical enhancement of visual saliency at a low perceptual level to be behaviorally relevant (mean RTs around 600 ms; Constable & Becker, 2017). Given this premise, relatively faster reactions may then exhibit lateralization of CP to the RVF.…”

Misconceptions About Colour Categories

“…There is some evidence that lateralized categorization may be produced independent of linguistic categories, suggesting that the lateralization is due to differences in attention to the visual fields (Alvarez, Clifford, Holmes, & Franklin, 2012). Others have argued that the lateralization of category effects depends on the time course of perceptual processing Constable & Becker 2017). Nevertheless, it remains an open question why lateralisation was found in some but not in other studies.…”