How fMRI Technology Contributes to the Advancement of Research in Mental Imagery: A Review

Mental imagery involves the generation of images using information stored in long-term memory, as opposed to the extemporaneous registration of information by our senses, giving rise to introspective experiences, such as ‘seeing with the mind’s eye’, ‘hearing with the mind’s ear’, ‘smelling with the mind’s nose’. In the past four decades, there has been much debate regarding the extent to which key elements of perception rely upon mental images versus propositional knowledge of sensory principles. Two contrasting approaches were developed i.e. perceptual and propositional theories. According to the perceptual approach, mental imagery is supported by mechanisms and processes involved in the actual perception. It functions as a modal analogue of that which is perceived by the senses (Kosslyn et al., 2006). Thus, mental images resemble perceptual information, e.g., visual images preserve both pictorial and spatial properties. According to the propositional approach, mental imagery is supported by abstract symbols of the sort used in a language-like system. It functions as an a-modal description of the external world (Anderson & Bower, 1973; Pylyshyn, 1981, 2002, 2003). In particular, mental images rely on a code, structured by rules and relationships, rather than on mere verbal descriptions. Therefore, these mental images are epiphenomena of thought: instead of exhibiting the sensory aspects that determine their analogical nature, they are affected by “cognitive permeability,” or the tacit knowledge of physical laws in the external world (Pylyshyn, 1981, 2002). These perspectives have primarily been investigated using visual imagery as a reference modality. After many years of behavioral research, the debate reached an impasse, as empirical evidence could only be explained by considering one of the two competitive approaches at a time (Kosslyn, 1980). The advent of neuroimaging techniques, particularly fMRI, offered the scientific community a new opportunity to solve the imagery debate. Unlike previous neuroimaging techniques, fMRI is capable of isolating many simultaneous and coordinated brain events with high spatial resolution. This facilitates the delineation of