Who are we?

We are researchers based in the Department of Psychology, Human Cognitive Neuroscience Group, University of Edinburgh. We have established links with Western General and Royal Victoria Hospitals to conduct our research. Below is a summary of the different forms of neglect, possible explanations thereof and what we are currently working on.

What is unilateral spatial neglect?

People showing unilateral perceptual neglect ignore one half of extra personal space, most commonly on the left, following a lesion in the right parietal lobe. 

Implicit processing in neglect:

Although patients with neglect ignore information on their left side, they appear to be affected indirectly by some of the ignored information. A classic example is that of patient PS (Marshall & Halligan, 1988), who was shown a picture of two houses, one above the other. One of the houses looked perfectly normal, while the other was depicted with flames on the left. The patient consistently reported that the houses were identical. However, when forced to choose in which house she would prefer to live, she tended to choose the house without flames, claiming this was a complete guess. 

What is representational neglect?

Neglect is not confined to impairments in reporting details of extra-personal space. It can also affect the mental representations of a scene, either recently perceived or from more remote past experience (Bisiach & Luzzatti, 1978). Some patients show only the representational form of neglect (Beschin et al., 1997). Neglect currently is interpreted as a deficit of directing attention. Different variants of the attentional theory have been proposed. However none of these theories addresses the issue of the cognitive architecture of the system that might be responsible for mental representations, nor do they adequately address how such a system might support covert direction of attention to different parts of the representation.

Working memory as a possible account of neglect:

Recent empirical evidence suggested that representational neglect might reflect a deficit in the visuo-spatial system within working memory (Della Sala et al., 2004). The idea was generalised by proposing a possible link between visuo-spatial attention and spatial working memory (Husain et al., 2001). Traditionally, working memory has been conceived as a form of transit store that acts to hold perceptual input on its way to long-term memory, its role being that of a “gateway” from perception to long-term memory. However, this view runs into difficulty when attempting to account for the wide range of evidence for implicit processing of sensory input that arises from studies of patients with neglect. Indeed, implicit processing in neglect demonstrates that the information, apparently not available within working memory, can be processed by means of access to stored knowledge in long-term memory and that sensory inputs are not necessarily held within working memory en route to long-term memory [8]. Rather, for those occasions on which a correct or a speeded response is generated, the stimuli activate stored knowledge in long-term memory at a level sufficient to constitute implicit processing.

A further implication of the gateway model is that damage to the transit function of the gateway should result in damage to processing of sensory input. For example, should the visuo-spatial functions of working memory be damaged as a result of brain injury or disease, and if those visuo-spatial functions act as a gateway between sensory input and the store of prior knowledge, then processing of sensory input should be impaired. This implication holds good when accounting for most published results from patients who show both perceptual and representational neglect. However, there have been reports of patients who presented with representational deficits in the absence of any impairment in perceiving extra personal space (Beschin et al., 2000). That is, these patients presented with persistent unilateral neglect limited to visual imagery, with no difficulty in reporting the contents of visually perceived scenes. Their pattern of spared and impaired abilities is rather difficult for the gateway model to address, even with the additional direct route between sensory input and stored knowledge (Della Sala et al., 2004).

Working memory as a mental work-space?

A possible alternative is that working memory could be considered as a system that remains separate from long term memory, but that deals with the products of activated long term memory traces. In this sense, working memory acts as a mental workspace for representing interpreted objects and scenes, allowing us to interact with and mentally manipulate those objects. Visuo-spatial working memory therefore would give us a temporary representation of the environment on which we can act mentally or which we can enact physically. The idea that visuo-spatial working memory is best viewed as a workspace rather than a gateway is supported by evidence from research on mental discovery (Barquero & Logie, 1999) which indicates that the contents of visuo-spatial working memory are interpreted, with semantic content drawn from stored knowledge before being made available within working memory. This is incompatible with working memory acting as a temporary buffer between perception and long-term memory. Material held in working memory may be manipulated in the absence of additional perceptual input, thereby reinforcing the concept of a mental workspace rather than only a temporary storage. This concept of working memory would allow us to account for implicit processing in neglect and would allow us to interpret representational neglect (Della Sala & Logie 2002).

An indirect link between visual perception and visuo-spatial working memory:

The double dissociations shown between pure perceptual and pure representational neglect imply that the processes of perception and the cognitive functions that support imagery may be less closely linked than is commonly assumed. Recently, we showed that the representational problems do not arise from impaired perceptual input, that the phenomena of perceptual neglect and representational neglect are best viewed as different disorders, and that the representational system can be damaged separately from the perceptual system (Denis et al., 2002).

Research questions in the current project:

By investigating patients affected by unilateral spatial neglect we aim to address the concept of visuo-spatial working memory as a feature of a mental workspace, rather than as the more traditional holding system for material that is being transferred from perception to long term memory, or as simply the sum total of currently activated traces from long-term memory. This will also allow us to better understand the detailed cognitive impairments suffered by such patients, and explore a possible theoretical interpretation of neglect which may lead to better insight into clinical management of these patients and informed rehabilitation programmes.

What remains unclear from previous research is precisely how patients with perceptual neglect access semantic knowledge about visual details presented in the neglected hemispace, or what implications there might be for the theoretical links between perception and mental representation. Moreover, there remains a debate as to whether representational neglect is best explained as a deficit in directing attention to the neglected side of a mental representation, or reflects damage to the representational system within working memory. We propose to test these alternative accounts directly by investigating whether representational neglect patients can perform mental manipulation and rotation tasks that would require the use of an intact attentional system.

Pseudoneglect:

In addition, we are interested in the phenomenon of pseudoneglect (Bowers & Heilman, 1980), which presents as an asymmetry in spatial awareness with the left side of space being favoured over the right side of space. Pseudoneglect occurs in the absence of neurological damage and has typically been explored using line bisection tasks (Jewell & McCourt, 2000). What remains unclear is whether pseudoneglect extends to spatial memory tasks of an auditory nature. We are currently exploring this possibility  in neurologically normal individuals.

 

References:

Barquero, B. & Logie, R.H. (1999). Imagery constraints on quantitative and qualitative aspects of mental synthesis. European Journal of  Cognitive Psychology, 11, 315-333.

Beschin, N., Basso, A., & Della Sala S. (2000). Perceiving left and imaging right. Cortex, 36, 401-414.

Beschin, N., Cocchini, G., Della Sala, S., & Logie, R.H. (1997). What the eyes perceive the brain ignores: a case of pure unilateral representational neglect. Cortex, 33, 3-26.

Bisiach, E., & Luzzatti, C. (1978). Unilateral neglect of representational space. Cortex, 14,129-133.

Bowers, D., & Heilman, K. M. (1980). Pseudoneglect: Effects of hemispace on a tactile line bisection task. Neuropscyhologia, 18 (4-5), 491 - 498.

Della Sala, S., & Logie, R.H. (2002). Neuropsychological impairments of visual and spatial working memory. In: Handbook of Memory Disorders. Wiley, Chichester, pp.271-292.

Della Sala, S., Logie, R.H., Beschin, N., & Denis, M. (2004).  Preserved visuo-spatial transformations in representational neglect. Neuropsychologia, 42, 1358-1364.

Denis, M., Beschin, N., Logie, R.H., & Della Sala, S. (2002). Visual perception and verbal descriptions as source for generating mental representations. Cognitive Neuropsychology, 19, 97-112.

Ellis, A.X., Della Sala, S., & Logie, R.H. (1996). The Bailwick of visuo-spatial working memory: evidence from unilateral spatial neglect. Cognitive Brain Research, 3, 71-78.

Husain, M., Mannan, S., Hodgson, T., Wojciulik, E., & Driver, J. (2001). Impaired spatial working memory across saccades contributes to abnormal search in parietal neglect. Brain, 124, 941-952.

Jewell, G., & McCourt, M. (2000). Pseudoneglect: a review and meta-analysis of performance factors in line bisection tasks. Neuropsychologia, 38 (1), 93-110.

Marshall, J., & Halligan, P.W. (1988). Blindsight and insight in visuo-spatial neglect. Nature, 336, 766-7.