Academic journal article Canadian Journal of Experimental Psychology

An Accrual Model for Primed Digit Classification

Academic journal article Canadian Journal of Experimental Psychology

An Accrual Model for Primed Digit Classification

Article excerpt

This article describes a chronometric experiment of digit classification with masked primes. EEG experiments have shown that the subliminal prime activates the cortex prior to the target signal, thusly modifying the response: Congruent primes lead to faster correct answers, while incongruent primes result in slower response. It is noticed that incorrect answers show an inverted effect: A congruent prime inhibits incorrect answers, and the reverse for incongruent primes. Within the evidence accrual paradigm, it is suggested that the prime activity in the motor cortex effectively behaves as a shift in the decision threshold. This model assumption is consistent with our experimental findings. The correct and incorrect answers and the error percentage are discussed.

Keywords: accrual model, subliminal prime, digits classification, response-priming effect, incorrect responses

(ProQuest: ... denotes formulae omitted.)

Since Moyer and Landauer's (1967) work, a substantial amount of research in cognitive psychology has focused on the processes underlying observers' judgement of numerical magnitude. In these experiments, participants are asked to choose the biggest or smallest number between two, or whether a random target number is bigger or smaller than a certain fixed standard number.

Considerable research effort in the past decade was devoted to understanding the cognitive process involved in two-choice tasks as an information process that evolves in time until it reaches a semantic decision. Progress in understanding these experiments has come through developing and testing models that deal with the underlying dynamics as a graduai accumulation of noisy information. Generically known as evidence accrual models (Petrusic, 1992) or as sequential sampling models (Ratcliff & Smith, 2004), these models paved the way for understanding performance in both speed and accuracy within a common theoretical framework.

In the simpler versions of these models, the evidence - information - is proportional to the difference between the two compared stimuli. Evidence and noise are additively accumulated over time toward a positive or a negative critical threshold, with a drift that depends on the sign and magnitude of the evidence. These models accrue noisy information sampled at discrete time steps as in a random walk process (Link, 1990; Page, Izquierdo, Saal, Codnia. & El Hast, 2004; Petrusic, 1992; Usher & McClelland, 2001) or continuously as in a diffusion process (Ratcliff, 1978). The decision, whether correct or incorrect, is associated with the achieved threshold, and the response time (RT) is associated with the number of accrual steps needed to reach it. Semantic closeness between the two compared stimuli reduces the initial evidence and consequently increases the time to access the critical threshold value. Thusly, this model performance offers a simple interpretation of the well-known distance effect; that is, the semantic closeness between two compared stimuli entails slower and less accurate responses. (Banks, Fujii, & Kayra-Stuart, 1976; Dehaene, 1989; Jamieson & Petrusic, 1975; Moyer & Landauer, 1967; Welford, 1960). Because of their built-in random characteristics, these models may predict the average RT of correct responses (correct RT), together with its standard deviation (SD), proportion of incorrect responses (error rate), and the RT of incorrect responses (incorrect RT).

A new dimension to study the dynamical processing of numbers has become available from classification experiments with masked primes (Dehaene et al., 1998; Forster & Davis, 1984; Greenwald. Abrams, Naccache, & Dehaene, 2003; Koechlin, Naccache, Block, & Dehaene, 1999; Kunde, Kiessel, & Hoffmann, 2003; Marcel, 1983; Naccache & Dehaene, 2001a; Naccache, Blandin, & Dehaene, 2002). The masks are intended to prevent the participant from developing strategic expectations on the target coming from visualising the prime (Neely, 1991). …

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