Compatibility between object size and response side in grasping: the left hand prefers smaller objects, the right hand prefers larger objects

The roles of symbolic and numerical representations in asymmetric visual search

This study aims to explore the impact of symbolic and numerical representations in asymmetric visual search. Heterogeneous and homogeneous mathematical units, letters, symbols and numbers were used in the first and second experiments, respectively. Target was searched among 6 or 12 stimuli. Analysis showed that the search efficiency was greatest in LaS (large among small), but the performance decreased significantly in SaS (small among small). Moreover, LaS was faster than SaL (small among large). However, SaL was faster than LaL (large among large) and LaL was faster than SaS. The findings of this study showed that the search efficiency was indirectly proportional to the number of stimuli. This implies that processing of visual stimuli of different sizes and appearance was asymmetric, all requiring varied attention. In summary, these findings strengthen the integration theory, similarity theory and guided search model.

Saccadic adaptation shapes perceived size: Common codes for action and perception

Recent findings suggest that perceptual and motor systems share common codes; for instance, perceived object location is known to correlate with motor changes in the oculomotor system. Here, we investigate whether modifying saccade amplitude affects object size perception. Participants saw in peripheral vision a test disk that could vary in size across trials. This disk was then replaced by a small target cross, which was the signal to make a saccade. After the saccade, the target cross was extinguished and replaced by a reference disk (thus seen in foveal vision). Participants had to compare the post- to the pre-saccade disk sizes. Psychometric functions were obtained before and after one session of 142 saccades made toward the cross that either stepped toward the fixation point during the saccade (backward adaptation group) or remained stationary (control group). In the experimental group, stepping the target cross toward fixation during saccades decreased movement amplitude, a phenomenon called saccadic adaptation. We observed a concurrent shift in the psychometric functions reflecting a decrease in perceived object size. Such a perceptual modification did not occur in the control group. Our results reveal that motor changes co-occur with changes in perceived object size. Unlike previous studies evaluating the impact of saccadic adaptation on perceived location, we measured here the perception of another spatial feature (the object size) that is not relevant for the sensorimotor transformation. Theoretical implications of the strong links between oculomotor parameters and object perception are discussed.

How does number magnitude influence temporal and spatial parameters of eye movements?

The influence of numerical processing on individuals' behavior is now well documented. The spatial representation of numbers on a left-to-right mental line (i.e., SNARC effect) has been shown to have sensorimotor consequences, the majority of studies being mainly concerned with its impact on the response times. Its impact on the motor programming stage remains less documented, although swiping movement amplitudes have recently been shown to be modulated by number magnitude. Regarding saccadic eye movements, the few available studies have not provided clear-cut conclusions. They showed that spatial-numerical associations modulated ocular drifts, but not the amplitude of memory-guided saccades. Because these studies held saccadic coordinates constant, which might have masked potential numerical effects, we examined whether spontaneous saccadic eye movements (with no saccadic target) could reflect numerical effects. Participants were asked to look either to the left or to the right side of an empty screen to estimate the magnitude (< or > 5) of a centrally presented digit. Latency data confirmed the presence of the classical SNARC and distance effects. More critically, saccade amplitude reflected a numerical effect: participants' saccades were longer for digits far from the standard (1 and 9) and were shorter for digits close to it (4 and 6). Our results suggest that beyond response times, kinematic parameters also offer valuable information for the understanding of the link between numerical cognition and motor programming.

Compatibility between response position and either object typical size or semantic category: SNARC- and MARC-like effects in primary school children

In two experiments, we administered two binary classification tasks to third- to fifth-grade students and found that either the conceptual size (Experiment 1) or semantic category (Experiment 2) of the target picture interacted with response position: Participants emitted faster and/or more accurate right- and left-side responses to stimuli referring to typically large and small objects (i.e., a SNARC [spatial-numerical association of response codes]-like effect) or to living and nonliving objects (i.e., a MARC [markedness association of response codes]-like effect), respectively. The effect of either stimulus dimension was present only when this dimension was the task-relevant one. These findings may be accounted for by the polarity compatibility principle. In binary classification tasks, one of the two relevant stimulus values (i.e., the dominant one) and one of the two response values would be coded as having a positive polarity, whereas the other would be coded as having a negative polarity. Response selection would be faster and/or more accurate when stimulus and response polarities are compatible. According to a less parsimonious hypothesis, the polarity principle would only explain the effect of the stimulus semantic category in Experiment 2, whereas the effect of stimulus conceptual size in Experiment 1 might be traced back to the fact that children spatially code the typical size of stimulus referents (even if only when the task requires accessing this stimulus dimension). Small and large objects would be represented relatively on the left and right, respectively, which would result in faster and/or more accurate responses when response position is compatible with the stimulus referent's position in this spatial representation.