A Case of Phantom Synchiric Percepts in Touch and Vision

After being presented with an ipsilesional stimulus, individuals with synchiria report both ipsilesional and contralesional sensation. Most published reports of synchiria are limited to a single modality. We report an individual with a right frontoparietal lesion (KG_591) who demonstrated synchiria subsequent to both visual and tactile stimulation. We tested KG_591 with various tasks in which she was presented with a stimulus on the left side, right side, both sides simultaneously, or no stimulation. On tactile trials, she reported tactile synchiric percepts on approximately 40% of right hand stimulation trials. Next, we projected visual stimuli either onto or away from her hands, in order to examine whether her phantom visual sensations were limited to personal space on the body. KG_591's synchiric percepts remained constant on or off of her hands, suggesting that her deficit was not limited to her body. Furthermore, as she does not report seeing phantoms in everyday life, we examined the effect of stimulus length on synchiric perception. Phantom synchiric percepts were most frequent after 250 millisecond visual stimuli, becoming less frequent with longer stimulus times. We discuss the implications of these and other results with regards to multisensory perception and the functional architecture that underlies synchiric perception