Unfolding visual lexical decision in time.

Laura Barca,Giovanni Pezzulo,Kevin Paterson

doi:10.1371/journal.pone.0035932

Abstract

Visual lexical decision is a classical paradigm in psycholinguistics, and numerous studies have assessed the so-called “lexicality effect" (i.e., better performance with lexical than non-lexical stimuli). Far less is known about the dynamics of choice, because many studies measured overall reaction times, which are not informative about underlying processes. To unfold visual lexical decision in (over) time, we measured participants' hand movements toward one of two item alternatives by recording the streaming x,y coordinates of the computer mouse. Participants categorized four kinds of stimuli as “lexical" or “non-lexical:" high and low frequency words, pseudowords, and letter strings. Spatial attraction toward the opposite category was present for low frequency words and pseudowords. Increasing the ambiguity of the stimuli led to greater movement complexity and trajectory attraction to competitors, whereas no such effect was present for high frequency words and letter strings. Results fit well with dynamic models of perceptual decision-making, which describe the process as a competition between alternatives guided by the continuous accumulation of evidence. More broadly, our results point to a key role of statistical decision theory in studying linguistic processing in terms of dynamic and non-modular mechanisms.

Highlights

The lexicality effect has been assessed in numerous psycholinguistic studies
In lexical decision tasks, when participants are required to briefly categorize items presented as words or nonwords, the Lexicality effect should be attenuated if the comparison is made between extremely lexical items and extremely nonlexical items, because the discrimination between stimuli does not require in-depth analysis but can be based on the visual processing of items [3]
Pseudowords and Low Frequency stimuli were slower than rich lexical items, with a mean reaction time difference for Pseudowords and High Frequency words about three times larger than the difference between Low and High frequency words

Summary

Introduction

The lexicality effect (i.e. faster and more accurate responses in processing words than nonwords) has been assessed in numerous psycholinguistic studies. Spivey [8] describes choices in terms of a continuous, dynamic competition between attractors (in this case, the two choice alternatives); these attractors ‘‘push’’ and ‘‘pull’’ mouse trajectories in a putative dynamic mental space An alternative to this (bottomup) evidence accumulation approach is the predictive coding view in which choice is essentially the minimization of the discrepancies between top-down predictions (e.g., lexical predictions) and bottom-up (perceptual) stimuli (see e.g., [9,10,11,12]). According to this model, the brain maintains a generative model of the sensorium, which encodes (probabilistic) hypotheses concerning the identity of observed stimuli (in this case, words or nonwords) and uses it to continuously generate (lexical) predictions. The selected hypothesis is the one that (after a sufficient number of iterations) minimizes a certain measure (in Friston’s account [10,11], free energy, or with some approximation, prediction error)

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Conclusion