Abstract: There has been a long-lasting debate about the essence of mental imagery. Some argues that the representations of mental imagery is language-like while others assumes it is depictive and perception-like. The availability of neuroimaging techniques, such as PET and fMRI, provides an opportunity to press this issue forward. With the development of analytical methods, decoding model and encoding model based on multivariate pattern analysis were used in exploring the neural mechanisms underlying mental imagery. Most of the neuroimaging studies involved in imagery debate were mainly focused on the activity of primary visual cortex (V1) in mental imagery. Here, we reviewed related neuroimaging studies and summarized three core questions in imagery debate. First, whether V1 could be activated during mental imagery? Some studies found the activation in V1 during mental imagery while some other studies failed finding V1 activation in the same process. Researchers have found several factors that could account for the discrepancy, including differences in baseline, tasks, and variation in the vividness of mental imagery across individuals. Therefore, despite the mixed results, it is safe to say that the activation of V1 is involved in mental imagery, even though it is weak. Second, could the activation in V1 organize in a topographically manner during mental imagery? Some researchers argued that in order to support the depictive view of imagery, it was important not only finding activation in V1 during mental imagery, but also these activation should be in a topographically organized manner. There was evidence revealed a retinotopic mapping of imagery, even when rule out the effect of attention. Their results suggest that visual imagery not only activated the V1 but also in a retinotopic manner comparable to perception. Third, what kinds of information are encoded in V1 during mental imagery? According to the predictive coding theory, when driven by top-down feedback, activity at any one location in V1 indicates the depicted visual features in the receptive fields. Previous studies found that the activated patterns between perception and imagery were similar, suggesting low-level features might be represented in imagery. More recently, a study using a voxel-wise encoding model and decoding approach found that low-level visual features were encoded during mental imagery. These results thus provided strong evidence for the depictive view of mental imagery, and facilitated the ending of imagery debate. Given the recent evidence, we can reasonably conclude that the imagery debate has been resolved. This opens the door to some perhaps more interesting questions. First, the vividness of mental imagery varies across individuals, however the neural mechanisms underlying the individual difference remain unclear. It is up to future research to probe the relationship between the brain mechanisms and the imagery ability. Second, does V1 play functional role in mental imagery? Researchers have not got consensus yet. Some argues that the activation of V1 during mental imagery is epiphenomenal, with no actual role. Others assume that V1 plays a functional role in generating images in mind, and the lesion of V1 would impair the performance in visual mental imagery. Third, how to reconstruct images in the mind from the neural activity pattern in the brain? Researchers have been able to reconstruct visual images of the stimuli from the neural activity pattern in the brain based on the established relationship between the stimuli properties and the neural activity patterns. Given low-level visual features also encoded in V1 in mental imagery, it is possible that we can find the corresponding relationship between imagery properties and activities in the brain, thus visualizing mental images.

Key words: primary visual cortex, mental imagery, representations, neuroimaging

摘要： 表象的信息表征方式一直是心理学研究的热点问题，脑成像技术在该问题的研究中发挥了巨大作用。本文以初级视觉皮层（V1）在表象表征方式研究中的作用为主线，系统梳理了基于脑成像技术开展的表象实质争论的核心问题，归纳分析了相关争论问题演绎发展的内在逻辑脉络，在此基础上指出了表象研究中需要进一步解决的关键问题，以期能够促进相关研究问题的进一步开展。

关键词: 初级视觉皮层, 表象, 表征, 脑成像