Neural correlates of perceptual completion of an artificial scotoma in human visual cortex measured using functional MRI

When a featureless achromatic target is placed on a textured pattern and steadily viewed in peripheral vision, after a few seconds it seems to fill-in with the surrounding texture, similar to the perceptual experience of patients with scotomas from damage to the visual pathways. Such "artificial scotomas" are thought to arise early in visual processing, but their neural basis in humans has not been fully explored. Here we used functional MRI to show that perceptual completion of an artificial scotoma is associated with selective reductions in activity in the retinotopic representation of the target in human primary visual cortex (V1) and area V2. Moreover, the persistence of signals associated with the target, even after perceptual completion had been reported, indicate the presence of a persistent representation of the now invisible target.

Self-management programs for adults with low vision: needs and challenges

OBJECTIVE

To explore the needs of individuals with low vision in order to inform the contents of a low vision self-management (SM) program and determine potential barriers to participation.

METHODS

Semi-structured interviews were conducted with 48 participants with low vision resulting different from eye conditions. Qualitative analysis was conducted in order to identify major themes.

RESULTS

All participants described a range of consequences as a result of vision loss including difficulties with functional activities, social interaction and emotional distress. Less than half were interested in attending a SM program. Barriers included practical reasons as well as a perceived lack of need and unclear or negative perceptions of such a program.

CONCLUSION

SM programs for low vision are a promising way to help address the range of difficulties experienced by this population if barriers to participation can be overcome.

PRACTICE IMPLICATIONS

SM programs should include vision-specific strategies, training in generic problem-solving and goal setting skills and how to cope with emotional reactions to vision impairment. Programs should be delivered and promoted in such a way to enhance access and encourage uptake by those with a range of vision loss in the community.

Activity in human V1 follows multisensory perception

When a single brief visual flash is accompanied by two auditory bleeps, it is frequently perceived incorrectly as two flashes. Such illusory multisensory perception is associated with increased activation of retinotopic human primary visual cortex (V1) suggesting that such activity reflects subjective perception [Watkins, S., Shams, L., Tanaka, S., Haynes, J.D., Rees, G., 2006. Sound alters activity in human V1 in association with illusory visual perception. Neuroimage. 31, 1247-1256]. However, an alternate possibility is that increased V1 activity reflects either fluctuating attention or auditory-visual perceptual matching on illusion trials. Here, we rule out these possibilities by studying the complementary illusion, where a double flash is accompanied by a single bleep and perceived incorrectly as a single flash. We replicate findings of increased activity in retinotopic V1 when a single flash is perceived incorrectly as two flashes, and now show that activity is decreased in retinotopic V1 when a double flash is perceived incorrectly as a single flash. Our findings provide strong support for the notion that human V1 activity reflects subjective perception in these multisensory illusions.

Neural correlates of perceptual filling-in of an artificial scotoma in humans

When a uniformly illuminated surface is placed eccentrically on a dynamic textured background, after a few seconds, it is perceived to disappear and be replaced by the background texture. Such texture filling-in is thought to occur in retinotopic visual cortex, but it has proven difficult to distinguish the contributions of invisible target and visible background to signals measured in these areas. Here, we used magnetoencephalography to measure time-dependent brain responses in human observers experiencing texture completion. We measured responses specifically associated with the filled-in target, by isolating neural population signals entrained at the frequency of flicker of the target. When perceptual completion occurred, and the target became invisible, there was significant reduction in the magnetoencephalography power at the target frequency over contralateral posterior sensors. However, even a subjectively invisible target nevertheless evoked frequency-specific signals compared with a no-target baseline. These data represent evidence for a persistent target-specific representation even for stimuli rendered invisible because of perceptual filling-in.

Involvement of prefrontal cortex in visual search

Visual search for target items embedded within a set of distracting items has consistently been shown to engage regions of occipital and parietal cortex, but the contribution of different regions of prefrontal cortex remains unclear. Here, we used fMRI to compare brain activity in 12 healthy participants performing efficient and inefficient search tasks in which target discriminability and the number of distractor items were manipulated. Matched baseline conditions were incorporated to control for visual and motor components of the tasks, allowing cortical activity associated with each type of search to be isolated. Region of interest analysis was applied to critical regions of prefrontal cortex to determine whether their involvement was common to both efficient and inefficient search, or unique to inefficient search alone. We found regions of the inferior and middle frontal cortex were only active during inefficient search, whereas an area in the superior frontal cortex (in the region of FEF) was active for both efficient and inefficient search. Thus, regions of ventral as well as dorsal prefrontal cortex are recruited during inefficient search, and we propose that this activity is related to processes that guide, control and monitor the allocation of selective attention.

Extra-classical receptive field effects measured in striate cortex with fMRI

The aim of this study was to measure the contextual influence of globally coherent motion on visual cortical responses using functional magnetic resonance imaging. Our motivation was to test a prediction from representational theories of perception (i.e. predictive coding) that primary visual responses should be suppressed by top-down influences during coherent motion. We used a sparse stimulus array such that each element could not fall within the same classical receptive field of primary visual cortex neurons (i.e. precluding lateral interactions within V1). This enabled us to attribute differences, in striate cortex responses, to extra-classical receptive field effects mediated by backward connections. In accord with theoretical predictions we were able to demonstrate suppression of striate cortex activations to coherent relative to incoherent motion. These results suggest that suppression of primary visual cortex responses to coherent motion reflect extra-classical effects mediated by backward connections.

Sound alters activity in human V1 in association with illusory visual perception

When a single brief visual flash is accompanied by two auditory bleeps, it is frequently perceived incorrectly as two flashes. Here, we used high field functional MRI in humans to examine the neural basis of this multisensory perceptual illusion. We show that activity in retinotopic visual cortex is increased by the presence of concurrent auditory stimulation, irrespective of any illusory perception. However, when concurrent auditory stimulation gave rise to illusory visual perception, activity in V1 was enhanced, despite auditory and visual stimulation being unchanged. These findings confirm that responses in human V1 can be altered by sound and show that they reflect subjective perception rather than the physically present visual stimulus. Moreover, as the right superior temporal sulcus and superior colliculus were also activated by illusory visual perception, together with V1, they provide a potential neural substrate for the generation of this multisensory illusion.

Cognitive Processes in Saccade Generation

The analysis of saccades offers an opportunity to study a number of different cognitive processes, such as visuospatial attention, working memory, and volitional conflict. A study of saccades in patients with visuospatial hemineglect, who performed a visual search task, showed repeated fixations on targets previously discovered, yet they often failed to retain the information that a particular target had previously been discovered. High-resolution structural brain scanning showed that this abnormality was due either to a lesion in the right intraparietal sulcus or the right inferior frontal lobe. Detailed analysis of the scanpaths suggested that the former location was associated with an accumulating impairment in remapping target locations across saccades or impaired memory of previously inspected target locations, whereas the latter location was more consistent with a failure to inhibit responses to rightward locations. When combined with a spatial bias to the right, such deficits might explain why many neglect patients often reexamine rightward targets, at the expense of items to their left. The functions of the supplementary eye field (SEF), in the medial frontal lobe, in relation to saccade generation are controversial. A series of studies in a patient with a focal lesion of the right SEF has indicated an important role for the SEF in the rapid self-control of saccadic eye movements and in set-switching (i.e., implementing control in situations of response conflict when ongoing saccadic plans have to be changed rapidly), rather than monitoring errors. In a recent fMRI study of normal subjects, it was shown that the SEF is involved in implementing the resolution of any volitional conflict, whereas other presupplementary motor areas are involved in the generation of volitional plans and processing volitional conflict.

Randomised-controlled trial of a fibre supplement on the symptoms of irritable bowel syndrome

The aim of this study was to assess the effect of coarse wheat bran on specific bowel function parameters and symptoms in patients with irritable bowel syndrome (IBS). A longitudinal, prospective, randomised, placebo-controlled trial was undertaken. The duration of treatment was eight to 12 weeks and this consisted of 10-20 g/day of coarse wheat bran or a low fibre placebo taken in addition to the normal diet. Twenty-eight outpatients fulfilling the Rome criteria for constipation-predominant IBS were recruited to the trial (14 in the treatment group; 14 in the placebo group). Twelve people completed the trial in the treatment group and ten in the placebo group. The main outcome measures included changes in symptoms recorded in a diary, changes in objective measurements of bowel function and subjective overall feelings of improvement. The bran group significantly increased their non-starch polysaccharide (NSP) intake over that of the placebo group (p < 0.05). Mean stool wet weight increased significantly more in the bran group than in the placebo group (p < 0.05), but other bowel function measurements and all recorded symptoms were not different. Many patients reported changes in bowel habit that were not reflected in the objective measurements. The addition of coarse wheat bran to the diet increased NSP ingestion and stool wet weight in this group of IBS patients, but no evidence was obtained that such treatment was of benefit to these patients, other than a placebo effect on symptoms.

Nasopharyngeal pH Monitoring in Chronic Sinusitis Patients Using a Novel Four Channel Probe

OBJECTIVE

To determine the prevalence of acid reflux into the nasopharynx in patients with chronic sinusitis.

STUDY DESIGN

Prospective study of patients presenting to a specialist rhinology practice with chronic sinusitis.

METHODS

Forty patients with chronic sinusitis underwent ambulatory 24 hour pH testing. The mean age of the patients was 56.3 years (25 Female, 15 Male). The studies were performed using a specially developed bifurcated 4 channel pH probe, incorporating 2 circumferential sensors positioned at the naso- and hypo-pharynx, and 2 unidirectional sensors positioned at the proximal and distal esophagus.

RESULTS

The circumferential band sensors yielded a stable recording largely free of artefact allowing meaningful recordings to be obtained from thirty-seven patients. Twelve patients (32.4%) were diagnosed with gastroesophageal reflux. A total of 809 reflux episodes were recorded. Of these, 596 (73.7%) reached the distal esophagus, with 187 (23.1%) and 24 (3.0%) reaching the proximal esophagus and hypopharynx respectively. Only 2 episodes (0.2%) were recorded in the nasopharynx. This occurred in 2 of 37 patients (5%).

CONCLUSIONS

Acid reflux into the nasopharynx is a rare event in patients with chronic sinusitis even though a significant proportion (32.4%) have abnormal 24 hour pH studies. It is likely that alternative mechanisms other than direct acid contact are involved in the pathogenesis of chronic sinusitis.

The internet

The growing use of email and the world wide web (WWW), by the public, academics, and clinicians-as well as the increasing availability of high quality information on the WWW-make a working knowledge of the internet important. Although this article aims to enhance readers' existing use of the internet and medical resources on the WWW, it is also intelligible to someone unfamiliar with the internet. A web browser is one of the central pieces of software in modern computing: it is a window on the WWW, file transfer protocol sites, networked newsgroups, and your own computer's files. Effective use of the internet for professional purposes requires an understanding of the best strategies to search the WWW and the mechanisms for ensuring secure data transfer, as well as a compendium of online resources including journals, textbooks, medical portals, and sites providing high quality patient information. This article summarises these resources, available to incorporate into your web browser as downloadable "Favorites" or "Bookmarks" from www.jnnp.com, where there are also freely accessible hypertext links to the recommended sites.

Subarachnoid haemorrhage: a clinical overview

Subarachnoid haemorrhage affects up to 9,000 people a year in the UK (Lindsay and Bone 1997) and is a devastating condition. Although many patients make a good physical recovery, some are left with cognitive and perceptual deficits. Early rehabilitation and support is essential, and caring for these patients and their families is a major challenge for nurses.