Mental imagery in synaesthesia

The current thesis addressed the question of whether an internally generated mental image can elicit a concurrent in grapheme colour synaesthesia; although there is experimental and anecdotal evidence that this is the case, to date this had not been systematically explored. As there are purportedly distinct object-based and spatial-based imagery processes it was necessary to explore the role different imagery processes may play. In Experiment 1 synaesthetes and matched control groups completed a grapheme-based object-imagery task against congruently and incongruently coloured backgrounds. Four synaesthetes, but none of the control groups, showed an effect of colour on task performance. In Experiment 2 and 3 synaesthetes (and matched controls for Experiment 2) completed a grapheme-based spatial-imagery task, with either the stimuli or background colour manipulated as before. In each experiment colour was found to interact with grapheme presentation format for two different synaesthetes. Experiments 1-3 therefore provided support for the idea that an internally generated mental image can elicit a concurrent. Importantly, the results suggested a difference in the way the concurrent generated from object or spatial imagery processes influenced task performance. Consequently Experiments 4 and 5 used a battery of comparable imagery tasks that had either an object or spatial rate-limiting imagery process. Manipulation of the task background colour again showed the variety of effects the concurrent generated with these different imagery processes can have on task performance. Overall the results of these experiments suggest that a concurrent can be elicited from both object and spatial imagery processes; important individual differences were found, and individual performance varied between tasks, suggesting the possible role of strategy effects. Models of synaesthesia need to be able to explain these differences and further studies are needed to address this issue of task approach.