The application of TMS in the study of perception
Perception is a constructive process dependent not only on the information inherent in a stimulus but also on the mental processing of the perceiver (Milner, 1998). The ability to use TMS to focus on specific cortical regions and disrupt neural processing in precise temporal windows, in conjunction with cognitive experimental techniques, has helped illuminate aspects of perception (Walsh and Rushworth, 1998) including:
- Speech/auditory perception
- Visual perception
- Spatial perception
- Motion perception
- Tactile perception
Ongoing research
Examples of the usefulness of TMS in perception studies are shown in recent research by D'Ausilio et al. (2009) and Kolvisto et al. (2010); D’Ausilio et al. administered TMS to motor cortex controlling lips and tongue during the discrimination of lip- and tongue-articulated phonemes. They found a neurofunctional double dissociation in speech sound discrimination supporting the idea that motor structures provide a specific functional contribution to the perception of speech sounds not just speech production.
Kolvisto et al. (2010) investigated the role of ‘late’ V1 activity in both aware and unaware visual motion perception. Participants were asked to make a forced-choice direction discrimination judgment on a coherently moving random-dot display and additionally rate their subjective awareness of the stimulus. Transcranial magnetic stimulation (TMS) was applied over the early visual cortex (V1/V2) after motion offset. Visual awareness was impaired at an ‘early’ (20 ms) and a ‘late’ (60 ms) stimulation time window. Participants' forced-choice direction discrimination performance on ‘unaware’ trials was above chance in No TMS baseline condition. Importantly, this performance was impaired by TMS over V1/V2 at the ‘late’ time window. The results indicate that recurrent extrastriate-V1 activity is necessary for both aware and unaware perception.
References
- Milner, Neuron, 1998
- D'Ausilio et al., Current Biology 2009
- Walsh and Rushworth, 1998
- Koivisto et al., NeuroImage, 2010
