Psychophysiological correlates of dynamic imagery
Dynamic imagery refers both to the imaginary transformation of objects and to the imagination of bodily movements. It is hypothesised that dynamic imagery involves both motoric and visuo-spatial representations and to demonstrate that they operate at the cortical level of the brain, subjects' electroencephalograms (EEG) were recorded whilst they performed a variety of dynamic imagery tasks. It was further hypothesised that cortical activity recorded during these tasks would vary as a function of individual differences in imagery ability. Due to the lack of consensus on the validity both of 'objective' and 'subjective' measures of imagery ability, both kinds of instrument were used in this thesis. It was hoped that the EEG would provide objective evidence of the validity of these measures. During imaginary transformation there was an increase in cortical activation over prefrontal and parieto-occipital cortex, suggesting that high-level motoric and visuo-spatial representations are active during this task. No difference was observed in the EEG of subjects classified according to subjective report but differences were observed when they were classified according to task performance. During movement imagery, an increase in activation over the pre-frontal and parietooccipital cortex was observed, supporting the involvement of motoric and visuo-spatial representations. However, significant results were only obtained when the experimental task imposed sufficiently high cognitive demands on subjects. Only objective measures of imagery ability were correlated to imagery related changes in cortical activity. These studies demonstrate the difficulty of modifying behavioural tasks to suit the restrictions of the psychophysiological environment. It is suggested that while having some benefit, the EEG presents major difficulties to the investigation of dynamic imagery. Given the restrictions of the experimental environment only simple movements are possible, thereby limiting the scope of experimental design.