Components of attention in synaesthesia‐congruent grapheme processing

The relationship between attention and colour‐grapheme synaesthesia has been investigated in numerous studies and from multiple viewpoints. One aspect, largely neglected in the literature, is how synaesthetes attend to stimuli, congruent with their experiences. Here we investigated whether the colours of briefly presented alphanumeric characters would differentially affect attentional parameters, dependent on congruence with the observers’ synaesthesia. Colour‐grapheme associations were mapped for 9 synaesthetes and psychophysical data collected in a mixed whole and partial report paradigm. Observers were presented with letters and digits and reported as many letter targets as possible, while ignoring digit distractors. The presented stimuli were either congruently coloured with each individuals synaesthetic experience, or in the inverse colour. We sampled performance over multiple exposure durations and target‐to‐distractor ratios and fitted the resulting data to a generic TVA‐based model (Bundesen, 1990). This model enabled us to estimate if the stimulus congruence affected discrete attentional parameters; namely the threshold for letter recognition, processing speed, selectivity and visual short‐term memory capacity. Memory capacity was significantly better under congruent conditions, an effect that may be due to the observers’ familiarity with the colour‐grapheme associations. However, there was no indication of a lowered perceptual threshold or more efficient selectivity under synaesthesia‐congruent conditions, but a general advantage in overall processing speed.
A control experiment showed that observers were not systematically biased towards processing, or responding to, congruent letters over incongruent ones. We discuss the implications of these results in the context of theories of visual attention and synaesthesia.