Abstract
The asymmetric distribution of human spatial attention has been repeatedly documented in both patients and healthy controls. Biases in the distribution of attention and/or in the mental representation of space may also affect some aspects of language processing. We investigated whether biases in attention and/or mental representation of space affect semantic representations. In particular, we investigated whether semantic judgments could be modulated by the location in space where the semantic information was presented and the role of the left and right parietal cortices in this task. Healthy subjects were presented with three pictures arranged horizontally (one middle and two outer pictures) of items belonging to the same semantic category. Subjects were asked to indicate the spatial position in which the semantic distance between the outer and middle pictures was smaller. Subjects systematically overestimated the semantic distance of items presented in the right side of space. We explored the neural correlates underpinning this bias using rTMS over the left and right parietal cortex. rTMS of the left parietal cortex selectively reduced this rightward bias. Our findings suggest the existence of an attentional and/or mental representational bias in semantic judgments, similar to that observed for the processing of space and numbers. Spatial manipulation of semantic material results in the activation of specialised attentional resources located in the left hemisphere.
Highlights
The asymmetrical nature of the cognitive and neural mechanisms that underlie the distribution of attention and/or mental representations when processing space has been documented in studies of healthy controls and neurological patients
To analyse the effect of left and right parietal repetitive transcranial magnetic stimulation (rTMS), a mixed factorial ANOVA was conducted to compare the performance of the different groups
In this paper we set out to investigate whether spatial variables, such as the spatial location in which semantic information is presented, modulate the performance of healthy participants in semantic judgments tasks
Summary
The asymmetrical nature of the cognitive and neural mechanisms that underlie the distribution of attention and/or mental representations when processing space has been documented in studies of healthy controls and neurological patients. Activation of the right posterior parietal cortex has been associated with bisection tasks involving both physical and mental number lines [20,21,22] It remains unclear whether the reported biases for space, numbers and alphabetical strings are observed for linguistic components without a left to right. The authors suggested that semantic information may modulate performance on a bisection task They argued that the semantic information activated the left hemisphere more strongly than the right hemisphere, and led to a rightward shift of attention away from the actual centre of the letter line [29,30]. The aim of our study was to investigate for the first time whether spatial variables, such as the spatial position (left vs right) in which semantic information is presented, modulate the performance of healthy participants in a semantic judgment task. Stimulation of the homologous regions in the left hemisphere had no effect [2,3]
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