Bernie Caessens

Numbers and space: A computational model of the SNARC effect

The SNARC (spatial numerical associations of response codes) effect reflects the tendency to respond faster with the left hand to relatively small numbers and with the right hand to relatively large numbers (S. Dehaene, S. Bossini, & P. Giraux, 1993). Using computational modeling, the present article aims to provide a framework for conceptualizing the SNARC effect. In line with models of spatial stimulus-response congruency, the authors modeled the SNARC effect as the result of parallel activation of preexisting links between magnitude and spatial representation and short-term links created on the basis of task instructions. This basic dual-route model simulated all characteristics associated with the SNARC effect. In addition, 2 experiments tested and confirmed new predictions derived from the model.

Processing of Abstract Ordinal Knowledge in the Horizontal Segment of the Intraparietal Sulcus

The anterior intraparietal sulcus, and more specifically its horizontal segment (hIPS), is known to play a crucial role in the cognitive representation of numerical quantity. Whether the involvement of hIPS is restricted to the processing of numerical information or generalizes to non-numerical ordinal dimensions remains an open question. Using functional magnetic resonance imaging during comparison tasks, we demonstrate that the hIPS is equally responsive to numbers and letters, indicating that hIPS is also involved in the representation and processing of non-numerical ordinal series. This extends the numerical processing function of IPS into the realm of abstract knowledge processing.

Automatic stimulus-response associations may be semantically mediated

Three experiments on numerical odd/even judgment are presented. In the first experiment, we show that tachistoscopically presented Arabic primes influence the reaction latencies (RTs) to Arabic targets in two ways: First, RTs to targets are longer when the prime and the target have a different parity status than when they share the same parity status, and second, on compatible trials, RTs are longer when the absolute distance between the prime and the target is larger. Experiments 2 and 3 extend the first finding by showing that the response compatibility effect is also obtained (1) when the primes are not part of the target set and the participants never reacted to them and (2) when the primes are presented in a different modality (verbal numerals) than are the targets (Arabic numerals). On the basis of these results, we conclude that, in masked priming, response codes are automatically activated by stimulus characteristics of the prime and that the activation of response codes is semantically mediated when the primes are meaningful.

Unconscious primes activate motor codes through semantics

Today, it is generally accepted that unconscious stimuli can activate a response code, which leads to a response congruency effect (RCE) on a subsequent target. However, it is not yet clear whether this is due to the semantic processing of the primes or to the formation of direct stimulus-response (S-R) associations bypassing the semantic system. Recently, it was shown that even novel primes, for which no direct S-R links exist, can also evoke an RCE that is in line with the activation of response codes through semantics. In these experiments, the authors examined 3 alternatives for this RCE from novel primes and report a novel effect in unconscious priming. First, the authors show that this effect is not limited to a small set of numerical stimuli but also extends to letter stimuli (Experiments 1-3). Second, the authors show that the RCE is not a side effect of the prime-target distance effect, as has been reported before (Experiments 1-2). Third, the authors found that, for RCE to occur, overlap at the motor level but not at the semantic level was crucial (Experiments 2-3). Finally, in addition, the results showed a category match priming effect independent of RCE. This last result is evidence that novel unconscious primes activate their semantic category prior to the target and might be considered a good marker for semantic processing.

Towards a common processing architecture underlying Simon and SNARC effects

It has been shown repeatedly that relatively small numbers are responded to faster with the left hand and relatively large numbers are responded to faster with the right hand. This so-called SNARC effect (Dehaene, Bossini, & Giraux, 1993) is thought to arise through activation of irrelevant spatial codes associated with the magnitude of the number. This conflict between irrelevant magnitude information and the response is conceptually similar to the well-known Simon effect. Recently, both Mapelli, Rusconi, and Umiltà (2003) and Keus and Schwarz (in press) directly compared both effects in a single task within the framework of the additive factor method (Sternberg, 1969). While Mapelli et al. found additive effects of SNARC and Simon levels, suggesting different processing stages, Keus and Schwarz found that the SNARC effect depended on the compatibility level of the Simon task leading them to propose a common origin at the response selection stage. In the present study we demonstrate in 2 experiments that the relationship between Simon and SNARC depends on the relevance of the magnitude code, thereby violating one of the core assumptions of the AFM. Instead we propose a temporal overlap model to interpret the relationship between these effects which allows to commensurate apparently divergent outcomes.

Inhibition and blindness to response-compatible stimuli: a reappraisal

Recent studies show that the preparation of an action can interfere with the concurrent detection and identification of objects that share features with this action, a phenomenon termed blindness to response-compatible stimuli. In order to account for the blindness effect, an integration mechanism for response features similar to the one suggested for object features has been proposed. In the present article, we propose an alternative explanation, namely an action-effect inhibition mechanism. This mechanism was demonstrated in two versions of a dual-task experiment using a primary stop-signal task. The results showed that when the primary response was withheld (signal-inhibit trials), this resulted in lower identification rates for compatible secondary task stimuli. On the other hand, we did not find any evidence for a blindness effect when the primary response was executed (no-signal trials). Additionally we found that identification rates depended on the time course of the inhibition process as estimated from our data. Consequently, the blindness effect seems to result from the requirement to inhibit the response, perhaps even if only temporary.

Voluntary and involuntary control over automatic processing in spatial congruency tasks: Editors' introduction

What makes an irrelevant stimulus attribute influence the processing of relevant stimulus and response attributes? Are these processes governed by the nature of the attributes and their mutual relationship (bottom-up processes) or are they strategically determined (top-down)? Cognitive psychology has a long tradition of over a century of research on these questions, which pertain to the domain of cognitive control. One of the most fruitful and interesting approaches to the topic of cognitive control has been through the study of congruency tasks. In congruency tasks the relationship between stimulus and response features is systematically varied, so that in some conditions relevant and irrelevant information indicate the same response while in other they lead to conflicting response tendencies. Differences in reaction times (RT) or accuracy measures between conditions with and without conflicting response tendencies are called congruency effects, and have been reported in most areas of cognitive psychology. Congruency effects have been demonstrated in a wide variety of tasks, with different S‐R sets and both within and between different modalities.