Beyond Sensation: The Cognitive Representation of Fingers

Details

Supervisors

Andres, Michael

Faculty

Faculté de psychologie, logopédie, sexologie et des sciences de la famille

Degree label

Master [120] en sciences psychologiques, à finalité approfondie

Abstract

Localizing tactile information on our body is of crucial importance to interact with the world and preserve our physical integrity. Tactile input is initially processed in the primary somatosensory cortex, which contains a somatosensory map of the body. However, this somatosensory map is distorted and therefore not sufficient to localize tactile stimuli on the body. A cognitive process is thus needed to shape the somatosensory map to a cognitive representation of the actual body shape, size, and posture. The properties of this representation remain largely unknown. Here, we investigated the structural and spatial characteristics of the cognitive representation of the hand in three finger recognition tasks. Experiment 1 tested whether fingers are cognitively represented as separate or continuous units of the hand space. Near-threshold tactile stimuli were applied on the medial or lateral side of each finger to investigate the respective influence of finger position over the hand and stimulus location over the finger on localization errors. The results showed a systematic error pattern based on finger position, irrespective of the side of stimulation, suggesting that fingers are represented as separate units. Experiment 2 and 3 investigated the frame of reference adopted when localizing tactile stimulation on one hand. Supra-threshold stimuli were applied on the fingers of the right hand while recording participants’ gaze behavior. Experiment 2 showed that in a palm-down position, stimulation of the fingers induces gaze shifts that reflect the location of the stimulated finger. These shifts were centered on the middle finger, presumably used as an anchor for finger recognition. Experiment 3 used the same paradigm with the hands palm-up to test whether anatomical or external coordinates are used for tactile localization. The gaze pattern observed in Experiment 2 was reversed in Experiment 3, suggesting the adoption of an external rather than anatomical frame of reference. Overall, this study shows that the cognitive representation of the hand is discrete, with each finger represented as a distinct unit of the hand space, and that finger identification involves the adoption of an external frame of reference, centered on the middle finger of the stimulated hand.