Grapheme-color synesthesia affects visual cognition in significant ways. The congruence or incongruence of physical stimuli with synesthetic color affects how quickly and accurately synesthetes respond to stimuli, and the induced color experience may help them memorize achromatic material and performance in visual search, much like physical stimulus features. It has been demonstrated that the content of visual memory can guide attention (e.g. Carlisle & Woodman, 2011). This effect can be measured in the response time costs or benefits related to the presence of memorized color in a visual search display. Retaining color information in memory biases attention towards that specific color in visual search, apparent by response time costs when a matching distractor is present, but a benefit when the target matches the retained color.
We investigated whether a synesthetic color is automatically represented in visual memory of observers with color-grapheme synesthesia, and consequently biases attention towards the synesthesia congruent stimuli. A group of synesthetes performed a memory task combined with a visual search for colored Landolt squares to explore this question. Each trial started with the presentation of an achromatic letter, followed by a visual search display. There were three types of search trials; 1) where the target color matched the color associated with the memorized letter, 2) where a distractor color matched the letter, and 3) where the associated color was absent from display. Finally, participants responded to memory probe to ensure that the letter was memorized.
We found no significant differences in response times dependent on synesthetically induced colors. However, there were clear costs and benefits of having physical colors in visual memory. This suggests that - unlike physical color - synesthetic colors are not automatically represented in visual memory.