Visual Perceptual Deficit Screening in Stroke Survivors: Evaluation of Current Practice in the United Kingdom and Republic of Ireland

PURPOSEVisual perceptual deficits are frequently underdiagnosed in stroke survivors compared to sensory vision deficits or visual neglect. To better understand this imparity, we evaluated current practice for screening post-stroke visual perceptual deficits.METHODSWe conducted a survey targeted at stroke clinicians involved in screening visual perceptual deficits across the United Kingdom and Republic of Ireland.RESULTSForty orthoptists and 174 occupational therapists responded to the survey. Visual perceptual deficit screening was primarily conducted by occupational therapists (94%), with approximately 75-100% of stroke survivors screened per month. Respondents lacked consensus on whether several common post-stroke visual deficits were perceptual or not. During screening, respondents primarily relied on self-reports and observation (94%), while assessment batteries (58%) and screening tools were underutilised (56%) and selected inappropriately (66%). Respondents reported lack of training in visual perception screening (20%) and physical/cognitive condition of stroke survivors (19%) as extremely challenging during screening.CONCLUSIONSVisual perceptual deficits are screened post-stroke at a similar rate to sensory vision or visual neglect. Underdiagnosis of visual perceptual deficits may stem from both reliance on subjective and non-standardised screening approaches, and conflicting definitions of visual perception held among clinicians. We recommend increased training provision and brief performance-based screening tools.

Echolocating bats detect but misperceive a multidimensional incongruent acoustic stimulus

Coherent perception relies on integrating multiple dimensions of a sensory modality, for example, color and shape in vision. We reveal how different acoustic dimensions, specifically echo intensity and sonar aperture (or width), are important for correct perception by echolocating bats. We flew bats down a corridor blocked by objects with different intensity–aperture combinations. To our surprise, bats crashed straight into large (aperture) walls with weak echo intensity as if they did not exist. The echolocation behavior of the bats indicated that they did detect the wall, suggesting that crashing was not a result of limited sensory sensitivity, but of a perceptual deficit. We systematically manipulated intensity and aperture by changing the materials and width of different reflectors, and we conclude that a coherent echo-based percept is created only when these two acoustic dimensions have certain relations which are typical for objects in nature (e.g., large and intense or small and weak reflectors). Nevertheless, we show that these preferred relations are not innate. We show that young pups are not constrained to these relations and that new intensity–aperture associations can also be learned by adult bats.

Characterizing developmental prosopagnosia beyond face perception: Impaired recollection but intact familiarity recognition

Converging lines of research suggests that many developmental prosopagnosics (DPs) have impairments beyond face perception, but currently no framework exists to characterize these impaired mechanisms. One potential extra-perceptual deficit is that DPs encode/retrieve faces in a distinct manner from controls that does not sufficiently support individuation. To test this possibility, 30 DPs and 30 matched controls performed an old/new face recognition task while providing confidence ratings, to which a model-based ROC analysis was applied. DPs had significantly reduced recollection compared to controls, driven by fewer ‘high-confidence target’ responses, but intact familiarity. Recollection and face perception ability uniquely predicted objective and subjective prosopagnosia symptoms, together explaining 51% and 56% of the variance, respectively. These results suggest that a specific deficit in face recollection in DP may represent a core aspect of the difficulty in confidently identifying an individual by their face.

Surprise-induced Deafness: Unexpected Auditory Stimuli Capture Attention to the Detriment of Subsequent Detection

Our attention is often captured by unexpected or unusual sounds. Such stimulus- driven control of attention can be adaptive, as potentially relevant events need to be quickly evaluated and acted upon. Attentional capture, however, comes with a cost: Ongoing tasks may be disrupted. In a series of seven experiments (n=773), we investigated the effects of task-irrelevant, rare, and relatively unexpected sounds (“surprise stimuli”) on probe detection in rapid auditory presentation (RAP) streams. Surprise stimuli caused “Surprise-induced Deafness” (SiD), a severe detection deficit that lasted for under one second within each trial and gradually habituated across several trials. SiD was sensitive to informational “surprise”, with larger deficits following stimuli that were infrequent or varied across trials. The effect also generalized: Natural sounds or constructed stimuli could disrupt detection of either spoken letters or simple tones. We also compared SiD to the auditory attentional blink (AAB), a similar paradigm in which goal-directed target processing disrupts probe detection. We found that the two deficits were weakly correlated. We conclude that SiD is a novel perceptual deficit that primarily reflects stimulus-driven attentional capture. It may involve other forms of attentional control as well, thereby reflecting multiple attentional influences on awareness.