"Unbinding" Imagery Via Attention

Despite the lack of direct evidence on the relationship between attention and imagery, at least two broad claims are well supported: first, attention is required for the maintenance of imagery, and second, imagery loads more heavily on attention than does perceptual processing.

Imagery clearly requires the use of executive functions, including attention (e.g., mental rotation; Tarr, 1995), perhaps in the form of Logie’s (2003) “inner scribe.” Also, attention in imagery is similar to perceptual attention: for example, the inspection of imaginary detail takes both time and attention, just as the scrutiny of perceptual images does. Space-based attention also seems important for imagery, as suggested by the similarity of imagery scanning times with those found in equivalent perceptual scanning tasks (see Pylyshyn, 2003, for a skeptical summary of these results, although his explanations are inconsistent with data described in a previous post, Neural Codes for Perception and Imagery). Finally, the time to form a mental image is dependent on the number of parts it has (Pylyshyn, 2003), suggesting that attention may also be at least partly feature- or object-based in imagery tasks, as it is in pattern recognition.

Because imagery lacks the bottom-up support inherent to perceptual images, it may require increased top-down biasing by attention. One would suspect that with such strong biasing, imagery would be particularly vulnerable to disruption by perceptual inputs. Indeed, the presentation of visual noise disrupts the vividness of imagery (Baddeley & Andrade, cited by Logie, 2003) and the effectiveness of imagery-based mnemonics (Quinn & McConnell, 1996, cited by Logie, 2003). Interestingly, visual noise does not disrupt items already stored in working memory (Logie, 2003), suggesting that perceptual input has a targeted disruptive effect on attention but not working memory functions.

Related evidence comes from a patient described by Bartolomeo (2002) who displayed classic unilateral neglect while drawing a butterfly from memory (i.e., drawing only the wing on the right side). However, when asked to redraw the image with closed eyes, he was capable of drawing a complete butterfly! This evidence is consistent with the speculative framework outlined above, in which the increased attentional biasing involved in imagery is particularly vulnerable to visual input. To put it another way, this patient’s tendency to attend to the right hemifield (RH) created a positive feedback loop: resulting in increased drawing in the RH, resulting in increased bottom-up support and hence more attention to the RH, resulting in yet more drawing in the RH, etc. This is a beautiful demonstration of the vulnerability imagery has to perceptual input, as a result of strong attentional biasing.

In summary, the relationship of imagery to attention is in some ways analogous with the relationship of pattern recognition to attention: there’s evidence for both location-based as well as feature/object-based attention in imagery tasks. Imagery may load more heavily on attention to sustain itself because it lacks bottom-up input. Because imagery requires this increasing top-down biasing, interference from perceptual input may be amplified. This conjecture is supported by evidence from the “butterfly patient” and the influence of visual noise on imagery tasks, described above.

One fascinating, but as yet unsupported hypothesis is that attention may be required for the "unbinding" of representations in mental imagery. Remember that attention is required for "binding," in which the neural processing of various object characteristics are brought together into a single, unitary representation. As discussed previously, the flow of perceptual information is reversed in mental imagery: neural data goes from long term memory to primary visual areas, rather than the other way around. It may be that attention is required in the process of "decompressing" visual data from the representational format of long term memory, or in other words, the "unbinding" of the representation from long-term memory into a mental "image" that is supported by activity in primary visual areas.

Related Posts:
Neural Codes for Perception and Imagery
Dissociations between Perception and Imagery
An Information Processing Approach to Mental Imagery
Attention: The Selection Problem
The Binding Problem

References:

Bartolomeo P. (2002) The relationship between visual perception and visual mental imagery: a reappraisal of the neuropsychological evidence. Cortex. 2002 Jun;38(3):357-78.

Logie, RH (2003). Spatial and Visual Working Memory: A Mental Workspace. The Psychology of Learning and Motivation. Volume 42. Academic Press. 37-38

M. Tarr, (1995) "Rotating objects to recognize them: A case study of the roleof viewpoint dependency in the recognition of three-dimensional obejcts," Psychonomic Bull. Rev., vol. 2, no. 1, pp. 55--82, 1995.

Pylyshyn Z. (2003) Return of the mental image: are there really pictures in the brain? Trends Cogn Sci. 2003 Mar;7(3):113-118.