The impact of visual imagery absence on fine-grained memory for object colour and size: an aphantasia study.

Visual memory and visual imagery are closely intertwined cognitive functions, yet whether memory necessarily deteriorates when imagery is impaired remains unresolved. Aphantasia, the inability to voluntarily generate mental images, provides a compelling model to address this issue. Previous reports of preserved or subtle memory deficits in aphantasia may stem from low task demands, coarse measures, or memory content lacking fine-grained requirements. To address this, we employed high-load paradigms and continuous precision measures with mixture modelling to assess colour memory-a domain requiring fine-grained representation. Experiment 1 (20 aphantasics, 20 controls) tested colour memory for six sets of 20 objects (15 meaningful, 5 meaningless). Meaningless objects were included to minimise verbal labelling. Colours were sampled from the Hue-Saturation-Value (HSV) space. Memory was assessed with a continuous colour wheel and analysed using mixture modelling that decomposed response errors into retrieval success (whether a colour was retrieved) and precision (how accurately it was remembered). Results revealed that aphantasic individuals showed markedly larger errors than controls, driven by reduced retrieval success rather than precision. Moreover, error magnitude and retrieval success correlated with several imagery dimensions (e.g., object imagery, spontaneous imagery use), whereas retrieval precision did not. Experiment 2 (18 aphantasics, 20 controls) further tested whether deficits extend beyond colour using an analogous size-memory task. No group differences or imagery-memory correlations were observed. These findings provide initial evidence that visual imagery supports retrieval success, but not retrieval precision, in accessing object colour memory, and that this role may not extend equally to all object features.