Somatosensory amplification and illusory tactile sensations

Experimental studies have demonstrated that it is possible to induce convincing bodily distortions in neurologically healthy individuals, through cross-modal manipulations; such as the rubber hand illusion (Botvinick and Cohen, 1998), the parchment skin illusion (Jousmaki and Hari, 1998) and the Somatic Signal Detection Task (SSDT; Lloyd et al., 2008). It has been shown previously with the SSDT that when a tactile stimulus is presented with a simultaneous light flash, individuals show both increased sensitivity to the tactile stimulus, and the tendency to report feeling the stimulus even when one was not presented; a tendency which varies greatly between individuals but remains constant over time within an individual (McKenzie et al., 2010). Further studies into tactile stimulus discrimination using the Somatic Signal Discrimination Task (SSDiT) have also shown that a concurrent light led to a significant improvement in people’s ability to discriminate ‘weak’ tactile stimuli from ‘strong’ ones, as well as a bias towards reporting any tactile stimulus as ‘strong’ (Poliakoff et al., in preparation), indicating that the light may influence both early and later stages of processing. The current study investigated whether the tendency to report higher numbers of false alarms when carrying out the SSDT is correlated with the tendency to experience higher numbers of cross-modal ‘enhancements’ of weak tactile signals (leading to classifications of ‘weak’ stimuli as strong, and ‘strong’ stimuli as ‘stronger’). Results will be discussed.