The Influence of Eye Closure on Somatosensory Discrimination: A Trade-off Between Simple Perception and Discrimination.

We often close our eyes to improve perception. Recent results have shown a decrease of perception thresholds accompanied by an increase in somatosensory activity after eye closure. However, does somatosensory spatial discrimination also benefit from eye closure? We previously showed that spatial discrimination is accompanied by a reduction of somatosensory activity. Using magnetoencephalography, we analyzed the magnitude of primary somatosensory (somatosensory P50m) and primary auditory activity (auditory P50m) during a one-back discrimination task in 21 healthy volunteers. In complete darkness, participants were requested to pay attention to either the somatosensory or auditory stimulation and asked to open or close their eyes every 6.5 min. Somatosensory P50m was reduced during a task requiring the distinguishing of stimulus location changes at the distal phalanges of different fingers. The somatosensory P50m was further reduced and detection performance was higher during eyes open. A similar reduction was found for the auditory P50m during a task requiring the distinguishing of changing tones. The function of eye closure is more than controlling visual input. It might be advantageous for perception because it is an effective way to reduce interference from other modalities, but disadvantageous for spatial discrimination because it requires at least one top-down processing stage.