Probing the unimaginable: The impact of aphantasia on distinct domains of visual mental imagery and visual perception

How do individual variations in the vividness of visual mental imagery impact different imagery domains, such as object shape, color, written words, faces, and spatial relationships? To address this question, we conducted a study with 117 healthy participants who reported different levels of imagery vividness, to examine how individual variations in the vividness of visual mental imagery affect different imagery domains, such as object shape, color, written words, faces, and spatial relationships. Of these participants, 44 reported experiencing absent or nearly absent visual imagery, a condition known as "aphantasia". These individuals were compared to those with typical (N = 42) or unusually vivid (N = 31) imagery ability. We used an online version of the French-language Battérie Imagination-Perception (eBIP), which consists of tasks tapping each of the above-mentioned domains in visual imagery and in visual perception. We recorded the accuracy and response times (RTs) of participants' responses. Bayesian analyses showed that there was a very high level of confidence that aphantasic participants had similar accuracy on all tasks compared to the other groups (BF = 0.02). However, their RTs were slower in both imagery and perceptual tasks (BF = 266), and they had lower confidence in their responses on perceptual tasks (BF = 7.78e5). A Bayesian regression analysis revealed that there was an inverse correlation between subjective vividness and RTs for the entire participant group. The pattern was similar in all the explored domains. The findings suggest that individuals with congenital aphantasia experience a slowing in processing visual information in both imagery and perception, but the precision of their processing remains unaffected. The observed performance pattern lends support to the ideas that congenital aphantasia is primarily a deficit of phenomenal consciousness, or that it employs alternative strategies other than visualization to access preserved visual information.