The role of orthographic neighbourhood effects in lateralized lexical decision: a replication study and meta-analysis

Abstract

The effect of orthographic neighbourhood size (N) on lexical decision reaction time differs when words are presented in the left or right visual fields. Evidence suggests a facilitatory N effect (i.e., faster reaction times for words with larger neighbourhoods) in the left visual field. However, the N effect in the right visual field remains controversial: it may have a weaker facilitative role or it may even be inhibitory. In a pre-registered online experiment, we replicated the interaction between N and visual field and provided support for an inhibitory N effect in the right visual field. We subsequently conducted a pre-registered systematic review and meta-analysis to synthesise the available evidence and determine the direction of N effects across visual fields. Based on the evidence, it would seem the effect is inhibitory in the right visual field. Furthermore, the size of the N effect is considerably smaller in the right visual field. Both studies revealed considerable heterogeneity between participants and studies, and we consider the implications of this for future work.

Keywords: Cerebral hemisphere; Laterality; Lateralized presentation; Orthographic neighbourhood effects; Replication; Systematic review and meta-analysis.

Figure 1. A schematic illustration of the SERIOL model, based on descriptions in Whitney (2004) and Whitney & Lavidor (2005).

Here, fixation falls between ‘O’ and ‘W’ with letters in each visual field projecting to the contralateral hemisphere. An acuity gradient is observed at the retina and the edge level (in V1 / V2). In the right hemisphere (but not the left), there is increased bottom-up excitation and left-to-right lateral inhibition, which reverses the acuity gradient to a spatial gradient at the feature level (in V4). Feature information is transferred from the right to left hemisphere, so that at the letter level (in the ventral occipitotemporal cortex, vOT) the serial order of letters in the word is represented by the activation for each letter. Activity spreads across potential matches at the word level (in the left temporal lobe), and top-down excitation back to the letter level facilitates word recognition.

Figure 2. Plots for pre-registered analyses.

Left: violin plots of RT for high- and low-N words in the left visual field (A), central visual field (B), and right visual field (C). The horizontal band reflects the mean in each experimental condition. Solid black lines correspond to low-N and dashed grey lines correspond to high-N. Right: Means across experimental conditions in the current study and Perea, Acha & Fraga (2008). Both datasets show a facilitatory N effect in the left visual field (D), a small facilitatory effect in the central visual field (E), and an inhibitory N effect in the right visual field (F). LVF, left visual field; CVF, central visual field; RVF, right visual field.

Figure 3. Plots for exploratory analyses.

(A) Reaction time differences (ms) [high N - low N] in each visual field. Dots represent individual participants’ data while the boxplot shows the median and interquartile ranges. The horizontal dashed black line represents zero, or no N effect. (B), (C), and (D) show scatterplots for the participants’ reaction time difference (ms) and laterality index in the left, central, and right visual fields respectively. The solid and dashed lines represent the relationship between the two variables. The shaded grey region represents 95% CIs.

Figure 4. Flowcharts of the literature search process.

(A) Our initial search of the literature. (B) Our forward search of the cited literature from eligible studies.

Figure 5. Forest plot of the N effect in the (A) left visual field and the (B) right visual field.

Plotted are the observed study means and 95% CI. The size of squares is proportional to the weight of each study in the analysis (i.e., the inverse of the within-study variance of the sampling distribution).