Power calculations in single-case neuropsychology: A practical primer

Practical routes to preregistration: a guide to enhanced transparency and rigour in neuropsychological research

Preregistration is the act of formally documenting a research plan before collecting (or at least before analysing) the data. It allows those reading a final research report to know which aspects of a study were decided before sight of the data, and which were added later. This enables informed evaluation of the severity with which scientific claims have been tested. We, as the British Neuropsychological Society Open Research Group, conducted a survey to explore awareness and adoption of open research practices within our field. Neuropsychology involves the study of relatively rare or hard-to-access participants, creating practical challenges that, according to our survey, are perceived as barriers to preregistration. We survey the available routes to preregistration, and suggest that the barriers are all surmountable in one way or another. However, there is a tension, in that higher levels of bias control require greater restriction over the flexibility of preregistered studies, but such flexibility is often essential for neuropsychological research. Researchers must therefore consider which route provides the right balance of rigour and pragmatic flexibility to render a preregistered project viable for them. By mapping out the issues and potential solutions, and by signposting relevant resources and publication routes, we hope to facilitate well-reasoned decision-making and empower neuropsychologists to enhance the transparency and rigour of their research. Although we focus neuropsychology, our guidance is applicable to any field that studies hard-to-access human samples, or involves arduous or expensive means of data collection.

The Graded Incomplete Letters Test (GILT): a rapid test to detect cortical visual loss, with UK Biobank implementation

Impairments of object recognition are core features of neurodegenerative syndromes, in particular posterior cortical atrophy (PCA; the 'visual-variant Alzheimer's disease'). These impairments arise from damage to higher-level cortical visual regions and are often missed or misattributed to common ophthalmological conditions. Consequently, diagnosis can be delayed for years with considerable implications for patients. We report a new test for the rapid measurement of cortical visual loss - the Graded Incomplete Letters Test (GILT). The GILT is an optimised psychophysical variation of a test used to diagnose cortical visual impairment, which measures thresholds for recognising letters under levels of increasing visual degradation (decreasing "completeness") in a similar fashion to ophthalmic tests. The GILT was administered to UK Biobank participants (total n=2,359) and participants with neurodegenerative conditions characterised by initial cortical visual (PCA, n=18) or memory loss (typical Alzheimer's disease, n=9). UK Biobank participants, including both typical adults and those with ophthalmological conditions, were able to recognise letters under low levels of completeness. In contrast, participants with PCA consistently made errors with only modest decreases in completeness. GILT sensitivity to PCA was 83.3% for participants reaching the 80% accuracy cut-off, increasing to 88.9% using alternative cut-offs (60% or 100% accuracy). Specificity values were consistently over 94% when compared to UK Biobank participants without or with documented visual conditions, regardless of accuracy cut-off. These first-release UK Biobank and clinical verification data suggest the GILT has utility in both rapidly detecting visual perceptual losses following posterior cortical damage and differentiating perceptual losses from common eye-related conditions.

Improving the DSM-5 approach to cognitive impairment: Developmental prosopagnosia reveals the need for tailored diagnoses

The Diagnostic Statistical Manual of Mental Disorders (DSM-5) recommends diagnosing neurocognitive disorders (i.e., cognitive impairment) when a patient scores beyond - 1 SD below neurotypical norms on two tests. I review how this approach will fail due to cognitive tests' power limitations, validity issues, imperfect reliabilities, and biases, before summarizing their resulting negative consequences. As a proof of concept, I use developmental prosopagnosia, a condition characterized by difficulties recognizing faces, to show the DSM-5 only diagnoses 62-70% (n1 = 61, n2 = 165) versus 100% (n1 = 61) through symptoms alone. Pooling the DSM-5 missed cases confirmed the presence of group-level impairments on objective tests, which were further evidenced through meta-analyses, thus validating their highly atypical symptoms. These findings support a paradigm shift towards bespoke diagnostic approaches for distinct cognitive impairments, including a symptom-based method when validated effective. I reject dogmatic adherence to the DSM-5 approach to neurocognitive disorders, and underscore the importance of a data driven, transdiagnostic approach to understanding patients' subjective cognitive impairments. This will ultimately benefit patients, their families, clinicians, and scientific progress.

Peripheral and bimanual reaching in a stroke survivor with left visual neglect and extinction

Whether attentional deficits are accompanied by visuomotor impairments following posterior parietal lesions has been debated for quite some time. This single-case study investigated reaching in a stroke survivor (E.B.) with left visual neglect and visual extinction following right temporo-parietal-frontal strokes. Unlike most neglect patients, E.B. did not present left hemiparesis, homonymous hemianopia nor show evidence of motor neglect or extinction allowing us to examine, for the first time, if lateralised attentional deficits co-occur with deficits in peripheral and bimanual reaching. First, we found a classic optic ataxia field effect: E.B.'s accuracy was impaired when reaching to peripheral targets in her neglected left visual field (regardless of the hand used). Second, we found a larger bimanual cost for movement time in E.B. than controls when both hands reached to incongruent locations. E.B.'s visuomotor profile is similar to the one of patients with optic ataxia showing that attentional deficits are accompanied by visuomotor deficits in the affected field.

Enhancing mathematics learning through finger-counting: A study investigating tactile strategies in 2 visually impaired cases

Finger-counting plays a crucial role in grounding and establishing mathematics, one of the most abstract domains of human cognition. While the combination of visual and proprioceptive information enables the coordination of finger movements, it was recently suggested that the emergence of finger-counting primarily relies on visual cues. In this study, we aimed to directly test this assumption by examining whether explicit finger-counting training (through tactile stimulation) may assist visually impaired children in overcoming their difficulties in learning mathematics. Two visually impaired participants (2 boys of 8.5 and 7.5 years) were therefore trained to use their fingers to calculate. Their pre- and post-training performance were compared to two control groups of sighted children who underwent either the same finger counting training (8 boys, 10 girls, Mage = 5.9 years; 10 kindergarteners and eight 1st graders) or another control vocabulary training (10 boys, 8 girls, Mage = 5.9 years; 11 kindergarteners and seven 1st graders). Results demonstrated that sighted children's arithmetic performance improved much more after the finger training than after the vocabulary training. Importantly, the positive impact of the finger training was also observed in both visually impaired participants (for addition and subtraction in one child; only for addition in the other child). These results are discussed in relation to the sensory compensation hypothesis and emphasize the importance of early and appropriate instruction of finger-based representations in both sighted and visually impaired children.

Left Cerebellar Lesions may be Associated with an Increase in Spatial Neglect-like Symptoms

Each cerebellar hemisphere projects to the contralateral cerebral hemisphere. Previous research suggests a lateralization of cognitive functions in the cerebellum that mirrors the cerebral cortex, with attention/visuospatial functions represented in the left cerebellar hemisphere, and language functions in the right cerebellar hemisphere. Although there is good evidence supporting the role of the right cerebellum with language functions, the evidence supporting the notion that attention and visuospatial functions are left lateralized is less clear. Given that spatial neglect is one of the most common disorders arising from right cortical damage, we reasoned that damage to the left cerebellum would result in increased spatial neglect-like symptoms, without necessarily leading to an official diagnosis of spatial neglect. To examine this disconnection hypothesis, we analyzed neglect screening data (line bisection, cancellation, figure copying) from 20 patients with isolated unilateral cerebellar stroke. Results indicated that left cerebellar patients (n = 9) missed significantly more targets on the left side of cancellation tasks compared to a normative sample. No significant effects were observed for right cerebellar patients (n = 11). A lesion overlap analysis indicated that Crus II (78% overlap), and lobules VII and IX (66% overlap) were the regions most commonly damaged in left cerebellar patients. Our results are consistent with the notion that the left cerebellum may be important for attention and visuospatial functions. Given the poor prognosis typically associated with neglect, we suggest that screening for neglect symptoms, and visuospatial deficits more generally, may be important for tailoring rehabilitative efforts to help maximize recovery in cerebellar patients.

A new way of classifying developmental prosopagnosia: Balanced Integration Score

Despite severe everyday problems recognising faces, some individuals with developmental prosopagnosia (DP) can achieve typical accuracy scores on laboratory face recognition tests. To address this, studies sometimes also examine response times (RTs), which tend to be longer in DPs relative to control participants. In the present study, 24 potential (according to self-report) DPs and 110 age-matched controls completed the Cambridge Face and Bicycle Memory Tests, old new faces task, and a famous faces test. We used accuracy and the Balanced Integration Score (BIS), a measure that adjusts accuracy for RTs, to classify our sample at the group and individual levels. Subjective face recognition ability was assessed using the PI20 questionnaire and semi structured interviews. Fifteen DPs showed a major impairment using BIS compared with only five using accuracy alone. Logistic regression showed that a model incorporating the BIS measures was the most sensitive for classifying DP and showed highest area under the curve (AUC). Furthermore, larger between-group effect sizes were observed for a derived global (averaged) memory measure calculated using BIS versus accuracy alone. BIS is thus an extremely sensitive novel measure for attenuating speed-accuracy trade-offs that can otherwise mask impairment measured only by accuracy in DP.

A new approach to diagnosing and researching developmental prosopagnosia: Excluded cases are impaired too

Developmental prosopagnosia is characterized by severe, lifelong difficulties when recognizing facial identity. Unfortunately, the most common diagnostic assessment (Cambridge Face Memory Test) misses 50-65% of individuals who believe that they have this condition. This results in such excluded cases' absence from scientific knowledge, effect sizes of impairment potentially overestimated, treatment efficacy underrated, and may elicit in them a negative experience of research. To estimate their symptomology and group-level impairments in face processing, we recruited a large cohort who believes that they have prosopagnosia. Matching prior reports, 56% did not meet criteria on the Cambridge Face Memory Test. However, the severity of their prosopagnosia symptoms and holistic perception deficits were comparable to those who did meet criteria. Excluded cases also exhibited face perception and memory impairments that were roughly one standard deviation below neurotypical norms, indicating the presence of objective problems. As the prosopagnosia index correctly classified virtually every case, we propose it should be the primary method for providing a diagnosis, prior to subtype categorization. We present researchers with a plan on how they can analyze these excluded prosopagnosia cases in their future work without negatively impacting their traditional findings. We anticipate such inclusion will enhance scientific knowledge, more accurately estimate effect sizes of impairments and treatments, and identify commonalities and distinctions between these different forms of prosopagnosia. Owing to their atypicalities in visual perception, we recommend that the prosopagnosia index should be used to screen out potential prosopagnosia cases from broader vision research.

A neurophenomenological fMRI study of a spontaneous automatic writer and a hypnotic cohort

PURPOSE

To evaluate the neurophenomenology of automatic writing (AW) in a spontaneous automatic writer (NN) and four high hypnotizables (HH).

METHODS

During fMRI, NN and the HH were cued to perform spontaneous (NN) or induced (HH) AW, and a comparison task of copying complex symbols, and to rate their experience of control and agency.

RESULTS

Compared to copying, for all participants AW was associated with less sense of control and agency and decreased BOLD signal responses in brain regions implicated in the sense of agency (left premotor cortex and insula, right premotor cortex, and supplemental motor area), and increased BOLD signal responses in the left and right temporoparietal junctions and the occipital lobes. During AW, the HH differed from NN in widespread BOLD decreases across the brain and increases in frontal and parietal regions.

CONCLUSIONS

Spontaneous and induced AW had similar effects on agency, but only partly overlapping effects on cortical activity.

E.L., a modern-day Phineas Gage: Revisiting frontal lobe injury

BACKGROUND

How the prefrontal cortex (PFC) recovers its functionality following lesions remains a conundrum. Recent work has uncovered the importance of transient low-frequency oscillatory activity (LFO; < 4 Hz) for the recovery of an injured brain. We aimed to determine whether persistent cortical oscillatory dynamics contribute to brain capability to support 'normal life' following injury.

METHODS

In this 9-year prospective longitudinal study (08/2012-2021), we collected data from the patient E.L., a modern-day Phineas Gage, who suffered from lesions, impacting 11% of his total brain mass, to his right PFC and supplementary motor area after his skull was transfixed by an iron rod. A systematic evaluation of clinical, electrophysiologic, brain imaging, neuropsychological and behavioural testing were used to clarify the clinical significance of relationship between LFO discharge and executive dysfunctions and compare E.L.´s disorders to that attributed to Gage (1848), a landmark in the history of neurology and neuroscience.

FINDINGS

Selective recruitment of the non-injured left hemisphere during execution of unimanual right-hand movements resulted in the emergence of robust LFO, an EEG-detected marker for disconnection of brain areas, in the damaged right hemisphere. In contrast, recruitment of the damaged right hemisphere during contralateral hand movement, resulted in the co-activation of the left hemisphere and decreased right hemisphere LFO to levels of controls enabling performance, suggesting a target for neuromodulation. Similarly, transcranial magnetic stimulation (TMS), used to create a temporary virtual-lesion over E.L.'s healthy hemisphere, disrupted the modulation of contralateral LFO, disturbing behaviour and impairing executive function tasks. In contrast to Gage, reasoning, planning, working memory, social, sexual and family behaviours eluded clinical inspection by decreasing LFO in the delta frequency range during motor and executive functioning.

INTERPRETATION

Our study suggests that modulation of LFO dynamics is an important mechanism by which PFC accommodates neurological injuries, supporting the reports of Gage´s recovery, and represents an attractive target for therapeutic interventions.

FUNDING

Fundação de Amparo Pesquisa Rio de Janeiro (FAPERJ), Universidade Federal do Rio de Janeiro (intramural), and Fiocruz/Ministery of Health (INOVA Fiocruz).

Dissociations in neuropsychological single-case studies: Should one subtract raw or standardized (z) scores?

This work tackles the problem of whether the dissociation between two performances in a single-case study should be computed as the difference between the raw or between the standardized (e.g. z) scores. A wrong choice can lead to serious inflation of the probability of finding false dissociations and missing true dissociations. Two common misconceptions are that (i) standardized scores are a universally valid choice, or (ii) raw scores can be subtracted when the two performances concern the same "task/test", otherwise standardized scores are better. These and other rules are shown to fail in specific cases and a solution is proposed in terms of in-depth analysis of the meaning of each score. The scores that should be subtracted are those that better reflect "deficit severities" - the latent, unobservable degrees of damage to the cognitive systems that are being compared. Thus explicit theoretical modelling of the investigated cognitive function(s) - the "scenario" - is required. A flowchart is provided that guides such analysis, and shows how a given neuropsychological scenario leads to the selection of an appropriate statistical method for detecting dissociations, introducing the critical concept of "deficit equivalence criterion" - the definition of what exactly a non-dissociation should look like. One further, overlooked problem concerning standardized scores in general (as measures of effect size, of which neuropsychological dissociations are just one example) is that they cannot be meaningfully compared if they have different reliabilities. In conclusion, when studying dissociations, increases in false-positive and false-negative risks are likely to occur when no explicit neuropsychological theory is offered that justifies the definition of what are to be considered as equivalent deficit severities in both performances, and which would lead to appropriate selection of raw, standardized, or any other type of score. More generally, the choice of any measure in any research context needs explicit theoretical modelling, without which statistical risks cannot be controlled.

Peripheral reaching in Alzheimer's disease and mild cognitive impairment

Recent evidence has implicated areas within the posterior parietal cortex (PPC) as among the first to show pathophysiological changes in Alzheimer's disease (AD). Focal brain damage to the PPC can cause optic ataxia, a specific deficit in reaching to peripheral targets. The present study describes a novel investigation of peripheral reaching ability in AD and mild cognitive impairment (MCI), to assess whether this deficit is common among these patient groups. Individuals with a diagnosis of mild-to-moderate AD, or MCI, and healthy older adult controls were required to reach to targets presented in central vision or in peripheral vision using two reaching tasks; one in the lateral plane and another presented in radial depth. Pre-registered case–control comparisons identified 1/10 MCI and 3/17 AD patients with significant peripheral reaching deficits at the individual level, but group-level comparisons did not find significantly higher peripheral reaching error in either AD or MCI by comparison to controls. Exploratory analyses showed significantly increased reach duration in both AD and MCI groups relative to controls, accounted for by an extended Deceleration Time of the reach movement. These findings suggest that peripheral reaching deficits like those observed in optic ataxia are not a common feature of AD. However, we show that cognitive decline is associated with a generalised slowing of movement which may indicate a visuomotor deficit in reach planning or online guidance.

Role of the Dorsal Posterior Parietal Cortex in the Accurate Perception of Object Magnitude in Peripheral Vision

Following superior parietal lobule and intraparietal sulcus (SPL-IPS) damage, optic ataxia patients underestimate the distance of objects in the ataxic visual field such that they produce hypometric pointing errors. The metrics of these pointing errors relative to visual target eccentricity fit the cortical magnification of central vision. The SPL-IPS would therefore implement an active “peripheral magnification” to match the real metrics of the environment for accurate action. We further hypothesized that this active compensation of the central magnification by the SPL-IPS contributes to actual object’ size perception in peripheral vision. Three optic ataxia patients and 10 age-matched controls were assessed in comparing the thickness of two rectangles flashed simultaneously, one in central and another in peripheral vision. The bilateral optic ataxia patient exhibited exaggerated underestimation bias and uncertainty compared to the control group in both visual fields. The two unilateral optic ataxia patients exhibited a pathological asymmetry between visual fields: size perception performance was affected in their contralesional peripheral visual field compared to their healthy side. These results demonstrate that the SPL-IPS contributes to accurate size perception in peripheral vision.