Abstract
Prior to goal-directed actions, somatosensory target positions can be localized using either an exteroceptive or an interoceptive body representation. The goal of the present study was to investigate if the body representation selected to plan reaches to somatosensory targets is influenced by the sensory modality of the cue indicating the target’s location. In the first experiment, participants reached to somatosensory targets prompted by either an auditory or a vibrotactile cue. As a baseline condition, participants also performed reaches to visual targets prompted by an auditory cue. Gaze-dependent reaching errors were measured to determine the contribution of the exteroceptive representation to motor planning processes. The results showed that reaches to both auditory-cued somatosensory targets and auditory-cued visual targets exhibited larger gaze-dependent reaching errors than reaches to vibrotactile-cued somatosensory targets. Thus, an exteroceptive body representation was likely used to plan reaches to auditory-cued somatosensory targets but not to vibrotactile-cued somatosensory targets. The second experiment examined the influence of using an exteroceptive body representation to plan movements to somatosensory targets on pre-movement neural activations. Cortical responses to a task-irrelevant visual flash were measured as participants planned movements to either auditory-cued somatosensory or auditory-cued visual targets. Larger responses (i.e., visual-evoked potentials) were found when participants planned movements to somatosensory vs. visual targets, and source analyses revealed that these activities were localized to the left occipital and left posterior parietal areas. These results suggest that visual and visuomotor processing networks were more engaged when using the exteroceptive body representation to plan movements to somatosensory targets, than when planning movements to external visual targets.
Highlights
In a game of “Simon Says”, spoken instructions such as “touch your elbow” can prompt movements towards a specified body location
Normalized directional reaching errors for the left and right fixation directions in the TACT-SOMA condition were not significantly different than zero (left: t(9) = 1.8, p = 0.099, d = 0.6; right: t(9) = -1.5, p = 0.170). These results provide evidence that gaze-dependent coding was used for sensorimotor transformations when movements were performed to auditory-cued visual and auditory-cued somatosensory targets
100 ms after the presentation of the auditory cue, during the participant’s reaction time, the green LED located on the pointing finger generated a 50 ms flash
Summary
In a game of “Simon Says”, spoken instructions such as “touch your elbow” can prompt movements towards a specified body location. The purpose of the present study was to examine if the modality of the stimulus indicating a somatosensory target’s position influences the body representation used to plan movements. We sought to examine the contribution of the exteroceptive and interoceptive body representations to sensorimotor transformations during motor planning in healthy individuals by evaluating reaching movements towards somatosensory targets cued by simple auditory and vibrotactile stimuli. In Experiment 1, to examine the body representation and sensorimotor transformations used to prepare movements to somatosensory targets, we asked participants to reach to somatosensory targets while looking at either a central fixation point or a peripheral fixation point (i.e., a gaze-shifted trial; see: [10,11,12,13,14,15,16]). To provide a reference of gaze-dependent reaching errors, participants performed movements to visual targets cued by an auditory stimulus
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