Grapheme-colour synaesthesia improves detection of embedded shapes, but without pre-attentive ‘pop-out’ of synaesthetic colour

Abstract

For people with synaesthesia letters and numbers may evoke experiences of colour. It has been previously demonstrated that these synaesthetes may be better at detecting a triangle made of 2s among a background of 5s if they perceive 5 and 2 as having different synaesthetic colours. However, other studies using this task (or tasks based on the same principle) have failed to replicate the effect or have suggested alternative explanations of the effect. In this study, we repeat the original study on a larger group of synaesthetes (n ¼ 36) and include, for the first time, an assessment of their self-reported colour experiences. We show that synaesthetes do have a general advantage over controls on this task. However, many synaesthetes report no colour experiences at all during the task. Synaesthetes who do report colour typically experience around one third of the graphemes in the display as coloured. This is more consistent with theories of synaesthesia in which spatial attention needs to be deployed to graphemes for conscious colour experiences to emerge than the interpretation based on 'pop-out'.

Automaticity in sequence-space synaesthesia: A critical appraisal of the evidence

“…This again mirrors arguments that the subjective colours of grapheme-colour synaesthetes arise at a 'cognitive' rather than 'perceptual level' (Gheri et al, 2008;Hupe et al, 2012;Mattingley, 2009;Nijboer et al, 2011;van Leeuwen et al, 2010;Ward et al, 2010).…”

How automatic are crossmodal correspondences?

“…The mere presence of the stimulus (or target) is sufficient to start the process, while awareness of its presence is unnecessary. This can, for example, be tested by looking for pop-out effects in visual search paradigms (Mattingley, 2009;Treisman, 2005;Ward, Jonas, Dienes, & Seth, 2010; though see Mack & Rock, 1998).…”

Do Synesthetic Colors Grab Attention in Visual Search?

“…Although many take the Gheri et al (2008) and Ward et al (2010) studies to have demonstrated that pre-attentive grapheme-color binding does not occur, we believe this conclusion is premature. The paradigm used for the Gheri et al study was designed only to provide positive evidence that pre-attentive binding does occur; its weakness lies in its inability to demonstrate that pre-attentive binding does not occur.…”

“…The Ward et al (2010) study also suffers from a significant limitation, as suggested by the authors of the study. The study found that synesthetes who claimed to perceive the majority of graphemes in the array as colored significantly outperformed synesthetes who reported little or no color experience.…”

“…However, the authors did not find a significant difference between synesthetes and controls under both conditions and concluded that binding does not occur pre-attentively. Ward et al (2010) conducted a revised version of the Ramachandran and Hubbard (2001a) and Hubbard et al (2005a, b) studies: in addition to the tasks included in the former studies, subjects were asked to report on their experiences of synesthetic colors after completing each task. Synesthetes scored higher than controls on visual search tasks, confirming the results of the former studies.…”