فراتر از تصویرسازی بصری: چگونه روش خاص تصویرسازی ذهنی در حس متقارن افزایش یافته است؟
|کد مقاله||سال انتشار||مقاله انگلیسی||ترجمه فارسی||تعداد کلمات|
|29695||2015||13 صفحه PDF||سفارش دهید||9775 کلمه|
Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Consciousness and Cognition, Volume 31, January 2015, Pages 73–85
Synesthesia based in visual modalities has been associated with reports of vivid visual imagery. We extend this finding to consider whether other forms of synesthesia are also associated with enhanced imagery, and whether this enhancement reflects the modality of synesthesia. We used self-report imagery measures across multiple sensory modalities, comparing synesthetes’ responses (with a variety of forms of synesthesia) to those of non-synesthete matched controls. Synesthetes reported higher levels of visual, auditory, gustatory, olfactory and tactile imagery and a greater level of imagery use. Furthermore, their reported enhanced imagery is restricted to the modalities involved in the individual’s synesthesia. There was also a relationship between the number of forms of synesthesia an individual has, and the reported vividness of their imagery, highlighting the need for future research to consider the impact of multiple forms of synesthesia. We also recommend the use of behavioral measures to validate these self-report findings.
Individuals with synesthesia (‘synesthetes’) have anomalous perceptual experiences: sensory stimulation in one modality induces additional atypical experiences within the same or different modality. Sound-color synesthetes, for example, experience colors in addition to sound when hearing auditory stimuli (Ward, Huckstep, & Tsakanikos, 2006). Synesthesia can also be induced by cognitive concepts, with one common form being grapheme-color synesthesia, in which color perceptions are induced by reading, hearing or thinking about letters, numbers and words (Ward, Li, Salih, & Sagiv, 2007). Other documented examples include word-taste synesthesia (taste experiences from words), sound-taste synesthesia (taste experiences from non-linguistic sounds), auditory–visual synesthesia (experiencing visual geometric shapes from sound) and so on (e.g., Beeli et al., 2005, Chiou et al., 2013, Ramachandran and Hubbard, 2001, Smilek et al., 2007, Ward and Simner, 2003 and Ward et al., 2006). In the majority of cases synesthesia is developmental, and has been present for as long as the synesthete can remember, though in a minority of cases synesthesia can be acquired after sensory loss (e.g. Steven & Blakemore, 2004) or neurological damage (e.g. Fornazzari, Fischer, Ringer, & Schweizer, 2012). Importantly, these additional synesthetic experiences occur without effort and are generally consistent over time (but see Simner, 2012). Over the past ten to fifteen years, our understanding of synesthesia has grown considerably (Hubbard, Brang, & Ramachandran, 2011) and there now exists a large body of research showing a range of neural and behavioral traits associated with the condition. For example, there are differences between the brains of synesthetes and non-synesthetes, with synesthetes having greater structural connectivity in several different regions (Jancke et al., 2009, Rouw and Scholte, 2007, Rouw and Scholte, 2010 and Zamm et al., 2013; for review see Rouw, Scholte, & Colizoli, 2011). There are also reported differences between synesthetes and non-synesthetes in the early sensory processing of visually presented stimuli (Barnett et al., 2008). Yet more research has started to explore the impact that synesthesia has on an individual’s cognitive and perceptual abilities, with some data suggesting that synesthetes may show enhanced abilities in certain aspects of memory (for a review see Rothen, Meier, & Ward, 2012) and sensory perception (Banissy, Walsh, & Ward, 2009). In the current study we ask whether synesthesia is also accompanied by enhanced abilities in mental imagery. Clearly, the key difference between synesthetes and non-synesthetes is that synesthetes have quasi-perceptual experiences in the absence of the usual external stimulation (e.g. they experience colors in the absence of visual stimulation). The quality of these experiences differs from synesthete to synesthete, with some describing their synesthetic experience (termed the “concurrent”) as vivid and tangible and others describing them as simply a ‘feeling of knowing’ ( Dixon et al., 2004, Hubbard et al., 2005 and Ward et al., 2007). Even so, descriptions of synesthetic percepts often seem similar to descriptions of mental images, and while there are some differences between synesthetic concurrents and mental images per se (e.g., synesthetic concurrents are typically reported to arise in a very involuntary manner, while at least some types of mental images are more effortful in character) we might nonetheless investigate the mental imagery abilities of synesthetes as compared to those of non-synesthetes. Specifically, since mental imagery can be thought of as “seeing in the mind’s eye in the absence of appropriate immediate sensory input” ( Kosslyn, Thompson, Kim, & Alpert, 1995, p. 1335), and since this description could also be applied to at least some synesthetic experiences, one might ask whether synesthetes’ mental imagery abilities are different to those of non-synesthetes (see also Simner, 2013). A small number of studies have started to explore the question of mental imagery in synesthesia. Barnett and Newell (2008) focused on self-reported vividness of visual imagery, comparing a group of synesthetes to a group of non-synesthete matched controls. Strength of visual imagery was reported using the Vividness of Visual Imagery Questionnaire (VVIQ, Marks, 1973), a self-report measure which asks respondents to generate a series of visual images of various scenes, and to rate how clear and vivid particular elements of these scenes are in the ‘mind’s eye’. The results showed that as a group, synesthetes reported significantly more vivid visual imagery than the control group. Following on from this, Price (2009) looked at the self-reported imagery of sequence-space synesthetes. These individuals experience sequenced units such as letters, numbers and months in particular spatial arrays, for example, envisaging months in an ellipse shape surrounding the torso ( Sagiv, Simner, Collins, Butterworth, & Ward, 2006). Using a different measure to the VVIQ, the Object-Spatial Imagery Questionnaire (OSIQ, Blajenkova, Kozhevnikov, & Motes, 2006), Price too found that sequence-space synesthetes reported stronger visual imagery than a control group (the same result was later found by Rizza & Price, 2012). Furthermore, Price found that compared to non-synesthetes, synesthetes reported using imagery more frequently on an everyday basis. Price’s study therefore supported Barnett and Newell’s conclusion that enhanced visual imagery may be a common trait associated with synesthesia. However, most of the synesthetes in the Barnett and Newell study had grapheme-color synesthesia, and the synesthetes in the Price study were sequence-space synesthetes, limiting their conclusions to only forms of synesthesia with visual–spatial concurrents. Furthermore, the self-report questionnaires used by these authors are themselves limited to visual–spatial forms of imagery. However, it is possible to form mental images across all sensory modalities, for example to form images of sounds, smells, tastes or tactile experiences. In the current study we therefore widen the assessment of synesthetes’ mental imagery to include different forms of synesthesia and different types of mental imagery (i.e., involving other sensory modalities). If individuals with visual forms of synesthesia have enhanced visual imagery, this could be due to their everyday experiences of visual concurrents – a sort of practice effect – since improvements in imagery with practice have been shown elsewhere (Noll et al., 1985 and Rodgers et al., 1991). If so, we would expect the enhanced imagery to be restricted to the modalities of the synesthesia. For example, a grapheme-color synesthete may report enhanced visual imagery, but would not be expected to report enhanced taste imagery. The idea that imagery enhancement may be restricted to the modalities involved in an individual’s synesthesia is supported by a recent study showing that synesthetes with visual concurrents showed enhanced visual perception but not enhanced tactile perception, and vice versa for synesthetes with tactile concurrents (Banissy et al., 2009). Of course it should also be noted that enhanced mental imagery within one modality could also be the trigger for synesthesia, rather than a consequence (see Price, 2013). Alternatively, synesthetes may experience enhanced imagery across all sensory modalities and this general enhanced imagery could result from more widespread structural or functional brain differences. As argued by Rouw et al. (2011), in their review of studies exploring brain areas involved in different forms of synesthesia, a broad network of areas is involved in synesthesia, extending beyond the modality-related sensory areas to other regions (e.g., those involved in feature binding and cognitive control). Rouw et al. concluded that a general ‘synesthetic constitution’ is likely to have effects beyond synesthesia. This broad constitution might affect imagery more broadly, given what we know about the neurological basis of imagery. Studies looking at the neural activity of mental imagery in the general population have shown both modality-specific and modality-independent activation. For example, although creating a visual image triggers neural activity in visual areas of the brain (and auditory images in auditory areas and so on), there may also be a ‘default mode network’, or core network, involved in imagery across all modalities (Daselaar et al., 2010 and McNorgan, 2012). Consequently, enhanced imagery could be unrelated to the specific synesthesia modality, and instead be related to more widespread cortical differences that affect the core network of brain areas involved in mental imagery across domains. Our current study is a large scale comparison of synesthetes’ and non-synesthetes’ self-reports of imagery across a range of imagery modalities. Synesthetes with synesthesia involving a variety of different sensory modalities completed a battery of questionnaires about their mental imagery experiences, along with age- and sex-matched controls. As used by previous studies on mental imagery in synesthesia, our measures included the VVIQ (Marks, 1973) to explore visual mental imagery, and the Subjective Use of Imagery Scale (SUIS, Reisberg, Pearson, & Kosslyn, 2003) to look at reports of everyday use of mental imagery. In addition, we used a self-report measure of auditory imagery (Clarity of Auditory Imagery Scale, CAIS; Willander & Baraldi, 2010) and olfactory imagery (Vividness of Olfactory Imagery Questionnaire, VOIQ; Gilbert, Voss, & Kroll, 1997). We also included the Vividness of Movement Imagery Questionnaire (VMIQ; Roberts, Callow, Hardy, Markland, & Bringer, 2008) which rates vividness of images of ‘external movement’ (e.g. imagining seeing yourself throw a ball), ‘internal movement’ (e.g. imagining what you would see when throwing a ball) and ‘kinesthetic movement’ (e.g. imagining what it would physically feel like to throw a ball). For imagery relating to touch, taste, and bodily sensations such as tiredness we used an adapted version of Bett’s Questionnaire Upon Mental Imagery (Sheehan, 1967). Table 1 summarizes the scales used with each concurrent/inducer modality. Table 1. Summary of scales used for each concurrent/inducer modality. Concurrent or inducer modality Scales Visual VVIQ, SUIS, VMIQ-I, VMIQ-E Auditory CAIS Tactile Touch imagery and Bodily Sensations subscales from Bett’s Questionnaire upon Mental Imagery, VMIQ-K Olfactory VOIQ Taste Taste imagery subscale from Bett’s Questionnaire upon Mental Imagery Table options The main focuses of our analysis were potential group differences between synesthetes and non-synesthetes in their total scores for each of these measures, to see if group differences exist in modalities beyond visual imagery. We were particularly interested to see whether there would be differences between specific sub-groups of synesthetes for particular image modalities (e.g. whether synesthetes with concurrents or inducers in the tactile modality report more vivid tactile imagery than other synesthetes). While we might expect synesthetes to report enhanced imagery in the modality of their concurrents, as found previously by Barnett and Newell with visual synesthetes reporting enhanced visual imagery, it is not so clear whether the same will be found for the modality of the inducer. Finally, synesthetes often report more than one form of synesthesia (Novich, Cheng, & Eagleman, 2011) meaning they experience inducers and concurrents across many different sensory modalities, as well as within the same modality. In this study we looked at the impact of having an inducer or concurrent within specific modalities (e.g., visual, tactile) but we also looked at the overall number of modalities affected in any given synesthete. If the vividness of an individual’s mental imagery is in some way related to them experiencing synesthesia, it may also be the case that the number of modalities involved may be related to mental imagery ability. We therefore wanted to examine whether there was a relationship between the reported vividness of imagery for each individual measure and the total number of modalities of synesthesia experienced by any individual. To date, very few studies (if any) have considered the impact of having multiple forms of synesthesia, and so this was a necessary, if exploratory, analysis.
نتیجه گیری انگلیسی
We calculated the total scores for each participant on each of the imagery scales. For the VVIQ, CAIS, and VOIQ scores could range from 16 to 80 and for all other scales the possible range was 12 to 60. Overall, we asked whether synesthetes report more vivid imagery in the same modality as their synesthesia, when compared to other synesthetes or non-synesthete controls. We conducted our analyses in three stages: first by considering synesthetes’ concurrents, second by considering their inducers, and third considering the impact of having both a concurrent and inducer in the same modality. For all stages of analysis, when a significant effect of group was found with one of the imagery scales, we conducted planned Bonferroni pairwise comparisons. We report analyses based on the complete sample of self-reported synesthetes, but also indicate below any differences in the pattern of our results when considering only the subset of 52 synesthetes that were independently verified for synesthesia. Please see Supplementary Material for individual scatterplots for each scale.