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Sensory representations in primary visual cortex are not sufficient for subjective imagery

DOI: 10.1101/2024.01.10.574972
Cabbai, G., Racey, C., Simner, J., Dance, C., Ward, J., & Forster, S. (n.d.). Sensory representations in primary visual cortex are not sufficient for subjective imagery. doi:10.1101/2024.01.10.574972

Abstract

The contemporary definition of mental imagery is characterized by two aspects: a sensory representation resembling, but not resulting from, perception, and an associated subjective experience. Neuroimaging demonstrated imagery-related sensory representations in primary visual cortex (V1) that show striking parallels to perception. However, it remains unclear whether these representations always reflect subjective experience, or they can be dissociated from it. We addressed this question by comparing sensory representations and subjective imagery among visualizers and aphantasics, the latter with an impaired ability to experience imagery. Importantly, to test for the presence of sensory representations independently of the ability to generate imageryon demandwe examined both spontaneous and voluntary imagery forms.Using multivariate fMRI, we tested for decodable sensory representations in V1 and subjective visual imagery reports that occurred either spontaneously (during passive listening of evocative sounds) or in response to the instruction tovoluntarilygenerate imagery of the sound content (always while blindfolded inside the scanner). Among aphantasics, V1 decoding of sound content was at chance during voluntary imagery, and lower than in visualizers, but it succeeded during passive listening, despite them reporting no imagery. In contrast, in visualizers, decoding accuracy in V1 was greater in voluntary than spontaneous imagery (while being positively associated with the reported vividness of both imagery types). Finally, for both conditions, decoding in precuneus was successful in visualizers but at chance for aphantasics. Together, our findings show that V1 representations can be dissociated from subjective imagery, while implicating a key role of precuneus in the latter.

Authors

  • Giulia Cabbai2
  • Chris Racey1
  • Julia Simner8
  • Carla Dance8
  • Jamie Ward2
  • Sophie Forster2

Understanding Mental Imagery: Insights from Visualizers and Aphantasics

Overview/Introduction

Mental imagery is the ability to create pictures in our minds without direct sensory input. This study explores how mental imagery works by examining two groups: visualizers, who can vividly picture things in their minds, and aphantasics, who struggle to do so. The research aims to understand whether the brain's sensory representations always match our subjective experiences of imagery.

Methodology

The study used multivariate fMRI to observe brain activity in participants as they listened to evocative sounds while blindfolded. Participants were divided into two groups: 26 visualizers and 24 aphantasics. They experienced two types of imagery:
  • Spontaneous imagery: Occurred naturally while passively listening to sounds.
  • Voluntary imagery: Participants were instructed to actively imagine the sounds.
The researchers focused on the primary visual cortex (V1) and the precuneus, two brain areas involved in processing visual information and imagery.

Key Findings

  • Visualizers: Showed higher brain activity in V1 during voluntary imagery compared to spontaneous imagery. Their brain activity was linked to how vividly they reported experiencing the imagery.
  • Aphantasics: Had brain activity in V1 during passive listening, despite reporting no imagery. However, their brain activity was at chance levels during voluntary imagery.
  • Precuneus Activity: Visualizers showed successful decoding of imagery in the precuneus, while aphantasics did not, suggesting this area plays a key role in the subjective experience of imagery.

Implications

These findings suggest that sensory representations in the brain (like those in V1) are not enough for the subjective experience of imagery. The precuneus appears crucial for this experience. This could change how we understand and study mental imagery, emphasizing the need to consider both spontaneous and voluntary imagery.

Limitations

  • The study's findings are based on a relatively small sample size.
  • The research focused on auditory-induced imagery, which may not fully represent other types of imagery experiences.
In conclusion, this study highlights the complexity of mental imagery and the distinct roles different brain areas play in creating our inner visual experiences. Understanding these processes could have broader implications for fields like psychology and neuroscience, particularly in understanding conditions like aphantasia.