Elsevier

Acta Psychologica

Volume 132, Issue 2, October 2009, Pages 190-200
Acta Psychologica

An fMRI investigation on image generation in different sensory modalities: The influence of vividness

https://doi.org/10.1016/j.actpsy.2009.06.009Get rights and content

Abstract

In the present fMRI study the issue of the specific cortices activation during imagery generation in different sensory modalities is addressed. In particular, we tested whether the vividness variability of imagery was reflected in the BOLD signal within specific sensory cortices. Subjects were asked to generate a mental image for each auditory presented sentence. Each imagery modality was contrasted with an abstract sentence condition. In addition, subjects were asked to fill the Italian version of the Questionnaire Upon Mental Imagery (QMI) prior to each neuroimaging session. In general, greater involvement of sensory specific cortices in high-vivid versus low-vivid subjects was found for visual (occipital), gustatory (anterior insula), kinaesthetic (pre-motor), and tactile and for somatic (post-central parietal) imagery modalities. These results support the hypothesis that vividness is related to image format: high-vivid subjects would create more analogical representations relying on the same specific neural substrates active during perception with respect to low-vivid subjects. Results are also discussed according to the simulation perspective.

Introduction

Mental imagery is considered to be an important component of conscious experience (Paivio, 1969), although it is held to usually occur with a lower intensity when compared to real perception (Fallgatter, Mueller, & Strik, 1997), since it is generated when perceptual information is retrieved from memory, and people are seeing with their “mind’s eye” (Kosslyn, 1994, Marks, 1973), or hearing with their “mind’s ear” (Halpern, 1988, Pitt and Crowder, 1992). In recent years, additional experimental evidence demonstrated that people are able to generate mental images also in tactile (Yoo, Freeman, McCarthy, & Jolesz, 2003), kinaesthetic (Jeannerod, 1995), olfactory (Djordjevic et al., 2004, Elmes, 1998), and gustatory (Kikuchi, Kubota, Nisijima, Washiya, & Kato, 2005) modalities.

Although many researchers argue that mental images in different sensory modalities preserve key elements of perceptual stimuli (Algom and Cain, 1991, Carrasco and Ridout, 1993, Decety and Michel, 1989, Halpern, 1988, Intons-Peterson, 1992, Kosslyn, 1980, Kosslyn et al., 1978, Parsons, 1994, Shepard and Metzler, 1971), others state that these representations rely on abstract symbols of the sort used in language (Anderson and Bower, 1973, Pylyshyn, 1973, Pylyshyn, 1979, Pylyshyn, 1981, Pylyshyn, 2002). This debate leads to the issue whether mental imagery and perception share the same mechanisms. The advent of neuroimaging techniques allowed researchers to shed light on the issues of modality-specificity and imagery format (Farah, 2000), addressing at least two different questions: (a) Is there an anatomical separation between the cortical areas serving imagery and those serving perception? (b) Are the areas used for imagery a subset of those engaged in perception?

Contrasting results have been provided so far. On one hand, some studies did not report the activation of early sensory areas during imagery tasks (Bunzeck et al., 2005, D’Esposito et al., 1997, Ishai et al., 2000a, Jahn et al., 2004, Mellet et al., 1998, Mellet et al., 2000). On the other hand, other studies found that perception and imagery share neural networks involving early sensory areas during visual (Amedi et al., 2005, Cui et al., 2007, Kosslyn et al., 1995, Kosslyn et al., 1999), auditory (Bunzeck et al., 2005, Hoshiyama et al., 2001), tactile (Yoo et al., 2003), olfactory (Bensafi et al., 2007, Djordjevic et al., 2005), gustatory (Kikuchi et al., 2005, Kobayashi et al., 2004), and kinaesthetic (Dechent et al., 2004, Lotze et al., 1999, Porro et al., 1996, Roth et al., 1996, Szameitat et al., 2007) imagery. Interestingly, a previous fMRI study from our group (Olivetti Belardinelli et al., 2004b, Olivetti Belardinelli et al., 2004a) investigated in the same experiment imagery for seven different sensory modalities (visual, auditory, kinaesthetic, olfactory, gustatory, tactile and somatic) triggered by visually presented sentences. Results revealed that all imagery modalities activated mainly two higher associative areas, located in the fusiform gyrus (BA 37) and in the inferior parietal lobule (BA 40), with a slightly different pattern across modalities.

Although these divergent results may be partly explained by considering small task differences (e.g., types of images, object categories, stimulus complexity, task requirements and modality of administration; Lambert, Sampaio, Scheiber, & Mauss, 2002), a major confound may be represented by individual differences in the ability to generate mental images. Traditionally, attempts to relate individual differences in imagery abilities were made using self-report questionnaires (Betts, 1909, Galton, 1880). Despite the general methodological criticisms for such methods, questionnaires were developed to test if vividness represents a general imagery ability (Sheehan, 1967) or a modality-specific characteristic (Switras, 1978, White et al., 1974). Furthermore, specific questionnaires were developed for visual (Marks, 1973), motor (Isaac, Marks, & Russel, 1986), auditory (Gissurarson, 1992) and olfactory (Gilbert, Crouch, & Kemp, 1998) imagery modalities.

In recent years neuroimaging techniques addressed the issue of the relationship between subjective and objective measures of imagery. For instance, some studies showed that subjective measures of vividness in visual imagery were associated with BOLD changes in the visual cortex (Amedi et al., 2005, Cui et al., 2007). In the present research, thus, we faced the question whether individual variability in imagery vividness, assessed by means of the Italian version on the Questionnaire Upon Mental Imagery, may be reflected in the activity of the corresponding early sensory cortex for each modality. We predicted that greater involvement of modality-specific cortices should be associated with higher subjective measures of vividness in each sensory modality, representing the specific sensory properties of vivid imagery.

Section snippets

Subjects

Nine, healthy right-handed university students (mean age = 25.2, SD = 3.7) participated in this study. Only female subjects were selected to reduce the gender-related variability that has been reported in imagery tasks (White, Ashton, & Braown, 1977). All of them had normal hearing and vision. Participants gave informed consent for a protocol approved by the local Institutional Ethics Committee and were paid for their participation.

Stimuli

Subjects were stimulated with a set of 96 (12 for each category)

Image preprocessing

Data were analysed using MATLAB 7.0 and SPM2 (http://www.fil.ion.ucl.ac.uk/spm). After discarding the first five images of each session to suppress T1 saturation effects, the 465 whole brain volume images (155 for each session) were realigned and resliced to correct for interscan head movements and then corrected for differences in acquisition time between slices during sequential imaging. The anatomical image of each subject was co-registered to the functional mean image calculated during the

Relevant activation for the whole sample

The one sample t-test analysis comparing each imagery modality versus the abstract condition was performed to explore what process imagery modalities have in common once critical components involved both in imagery and in the abstract condition are subtracted (e.g., task initiation and maintenance, attention, and working memory). In general, the activation of the left fusiform gyrus (BA37) was found for all the imagery modalities. The somatic imagery yielded also the activation of the right

Discussion

In the last decade, neuroimaging studies offered critical insights into the long standing mental imagery debate. In fact, the neural bases of mental image generation have been investigated in all the sensory modalities, showing that both modality-specific and a-specific areas are involved. Nevertheless, few studies focused on the differences or similarities for all imagery modalities and on the possible influence of vividness variability on cortical activity. In this study we tested whether the

Conclusions

According to our hypothesis, the level of imagery vividness in different sensory modalities may be related to differences of BOLD activity in modality-specific cortices. In other words, some of the neural processes underlying modality-specific perception may also be used in imagery when people are able to evoke vivid images. In particular we found modality-specific activation for visual, tactile, gustatory, kinaesthetic and somatic imagery modalities when subjects generated and maintained

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