Neural Correlates of Tactile Attention: Behavioural measures and event-related brain potentials of inhibition of return, exogenous and endogenous attention in touch
The studies presented in this thesis investigated the neural correlates of attention in touch. In particular, the electrophysiology of exogenous tactile processing and inhibition of return (IOR) - an area previously unexplored. In all studies a variation of the Posner cue-target paradigm was used. Typically, a cue was presented to the left or right hand. Following a stimulus onset asynchrony of 800 ms, a target would appear at the same or opposite hand. Behavioural results consistently demonstrated IOR when employing a simple target detection task, showing that IOR is a reliable phenomenon in touch. The concurrently recorded event related potentials (ERPs) demonstrated an early attention modulation of the N80 in all studies presented in this thesis, regardless of the presence or absence of IOR. This early component likely reflects processing of the exogenous lateralized cues. Following the N80, the attention modulations varied across studies. The conclusion to be drawn from this thesis is that not one particular ERP component is directly associated with IOR. Analysis of endogenous tactile attention (Chapter V) demonstrated modulations at the N140 and Nd components. Moreover, correlation analysis showed that larger ERP attention modulation was associated with a larger behavioural effect, demonstrating a novel relationship between ERP modulations and response time effects. Analysis of the cue-target interval has previously only been investigated during endogenous orienting. Here, and for the first time, an anterior directing attention negativity (ADAN) was demonstrated during exogenous orienting. This ADAN was unaffected by varying posture suggesting exogenous tactile attention and IOR are somatotopically coded. Indications of an external frame of reference were only demonstrated during shifts of endogenous attention, as indicated by the presence of a late directing attention positivity (LDAP) (endogenous counter-predictive task presented in Chapter V). The final study of this thesis (Chapter VI) demonstrated that varying visual perceptual load influenced tactile processing. Specifically, high perceptual load led to elimination of IOR. Moreover, the P100 for irrelevant tactile stimuli was significantly reduced in high versus low load condition. This suggests perceptual load may suppress irrelevant tactile stimuli relatively early (around 100 ms post stimuli onset) during tactile processing. Taken together, this thesis presents a series of experiments which map out effects of endogenous and exogenous attention and how these mechanisms interact, both through behaviour and underlying neural correlates.
BF Psychology, RC0321 Neuroscience. Biological psychiatry. Neuropsychiatry
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