Express Visuomotor Responses Reflect Knowledge of Both Target Locations and Contextual Rules during Reaches of Different Amplitudes.

When humans reach to visual targets, extremely rapid (∼90 ms) target-directed responses can be observed in task-relevant proximal muscles. Such express visuomotor responses are inflexibly locked in time and space to the target and have been proposed to reflect rapid visuomotor transformations conveyed subcortically via the tecto-reticulo-spinal pathway. Previously, we showed that express visuomotor responses are sensitive to explicit cue-driven information about the target, suggesting that the express pathway can be modulated by cortical signals affording contextual prestimulus expectations. Here, we show that the express visuomotor system incorporates information about the physical hand-to-target distance and contextual rules during visuospatial tasks requiring different movement amplitudes. In one experiment, we recorded the activity from two shoulder muscles as 14 participants (6 females) reached toward targets that appeared at different distances from the reaching hand. Increasing the reaching distance facilitated the generation of frequent and large express visuomotor responses. This suggests that both the direction and amplitude of veridical hand-to-target reaches are encoded along the putative subcortical express pathway. In a second experiment, we modulated the movement amplitude by asking 12 participants (4 females) to deliberately undershoot, overshoot, or stop (control) at the target. The overshoot and undershoot tasks impaired the generation of large and frequent express visuomotor responses, consistent with the inability of the express pathway to generate responses directed toward nonveridical targets as in the anti-reach task. Our findings appear to reflect strategic, cortically driven modulation of the express visuomotor circuit to facilitate rapid and effective response initiation during target-directed actions.SIGNIFICANCE STATEMENT Express (∼90 ms) arm muscle responses that are consistently tuned toward the location of visual stimuli suggest a subcortical contribution to target-directed visuomotor behavior in humans, potentially via the tecto-reticulo-spinal pathway. Here, we show that express muscle responses are modulated appropriately to reach targets at different distances, but generally suppressed when the task required nonveridical responses to overshoot/undershoot the real target. This suggests that the tecto-reticulo-spinal pathway can be exploited strategically by the cerebral cortex to facilitate rapid initiation of effective responses during a visuospatial task.

Schizotypy and perceptual span in a non-clinical sample: a virtual reality study.

INTRODUCTION: Individuals with high schizotypy or schizophrenia exhibit difficulties in distributing their attention across space, leading to a reduction in their "perceptual span" - the extent of visual space that can be attended to at once. In this study, we aim to explore the correlation between schizotypy and perceptual span in a non-clinical sample to investigate whether perceptual span correlates with schizotypy across its range. METHODS: Schizotypy was assessed in fifty-five participants using the Schizotypy Personality Questionnaire (SPQ; Raine, 1991). Participants were required to attend to two dynamic targets displayed in a head-mounted virtual reality display. Perceptual span was estimated as the lateral angle of separation between the two targets beyond which performance in the task dropped to threshold. RESULTS: Participants with higher schizotypy scores performed significantly worse on the task. Of all the factors associated with schizotypy, the shared variance between Disorganisation and Cognitive/Perceptual Factors was most predictive of task performance. CONCLUSION: The results support the hypothesis that schizotypy predicts perceptual span in non-clinical samples. Furthermore, the demonstration of a reduced perceptual span in individuals with higher trait schizotypy shows that variations in an individual's capacity to divide attention across space can be accurately captured using a virtual reality head-mounted display.

Symbolic cues enhance express visuomotor responses in human arm muscles at the motor planning rather than the visuospatial processing stage.

Humans can produce "express" (∼100 ms) arm muscle responses that are inflexibly locked in time and space to visual target presentations, consistent with subcortical visuomotor transformations via the tecto-reticulo-spinal pathway. These express visuomotor responses are sensitive to explicit cue-driven expectations, but it is unclear at what stage of sensory-to-motor transformation such modulation occurs. Here, we recorded electromyographic activity from shoulder muscles as participants reached toward one of four virtual targets whose physical location was partially predictable from a symbolic cue. In an experiment in which targets could be veridically reached, express responses were inclusive of the biomechanical requirements for reaching the cued locations and not systematically modulated by cue validity. In a second experiment, movements were restricted to the horizontal plane so that the participants could perform only rightward or leftward reaches, irrespective of target position on the vertical axis. Express muscle responses were almost identical for targets that were validly cued in the horizontal direction, regardless of cue validity in the vertical dimension. Together, these findings suggest that the cue-induced enhancements of express responses are dominated by effects at the level of motor plans and not solely via facilitation of early visuospatial target processing. Notably, direct corticotectal and corticoreticular projections exist that are well-placed to modulate prestimulus motor preparation state in subcortical circuits. Our results could reflect a neural mechanism by which contextually relevant motor responses to compatible visual inputs are rapidly released via subcortical circuits that are sufficiently along the sensory-to-motor continuum.NEW & NOTEWORTHY Express arm muscle responses to suddenly appearing visual targets for reaching rapid have been attributed to the tecto-reticulo-spinal pathway in humans. We demonstrate that symbolic cues before target presentation can modulate such express arm muscle responses compatibly with the biomechanics of the cued reaching direction and the cue validity. This implies cortically mediated modulation of one or more sensorimotor transformation nodes of the subcortical express pathway.

Visual-haptic integration, action and embodiment in virtual reality.

The current generation of virtual reality (VR) technologies has improved substantially from legacy systems, particularly in the resolution and latency of their visual display. The presentation of haptic cues remains challenging, however, because haptic systems do not generalise well over the range of stimuli (both tactile and proprioceptive) normally present when interacting with objects in the world. This study investigated whether veridical tactile and proprioceptive cues lead to more efficient interaction with a virtual environment. Interaction in the world results in spatial and temporal correlation of tactile, proprioceptive and visual cues. When cues in VR are similarly correlated, observers experience a sense of embodiment and agency of their avatars. We investigated whether sensorimotor performance was mediated by embodiment of the avatar hands. Participants performed a Fitts' tapping task in different conditions (VR with no haptics, active haptics, passive haptics, and on a real touchscreen). The active-haptic condition provided abstract tactile cues and the passive haptic condition provided veridical tactile and proprioceptive cues. An additional (hybrid haptics) condition simulated an ideal passive haptic system. Movement efficiency (throughput) and embodiment were higher for the passive than for the active and no-haptics conditions. However, components of embodiment (perceived agency and ownership) did not predict unique variance in throughput. Improved sensorimotor performance and ratings of presence and realism support the use of passive haptics in VR environments where objects are in known and stable locations, regardless of whether performance was mediated by the sense of embodiment.

Designing Virtual Reality Assisted Psychotherapy for Anxiety in Older Adults Living with Parkinson's Disease: Integrating Literature for Scoping.

Objective: This review integrates literature to discuss the potential use of virtual reality (VR) in treatment of anxiety in Parkinson's disease (PD) and inform next steps.Methods: A systematic search was performed to identify studies of VR use in PD, using four databases. Data were reported in accordance to the Preferred Reporting Items for Systematic reviews and Meta-Analyzes extension for Scoping Reviews (PRISMA-ScR).Results: Thirty-two studies met the inclusion criteria with four VR studies from the same study group directly assessing the effects of anxiety on motor symptoms in PD. Primary studies implementing a VR protocol in PD identified focus areas of understanding and alleviating freezing of gait (FOG), balance training, and cognitive and motor rehabilitation, and informed design considerations.Conclusion: VR in PD studies suggested established feasibility. With appropriate design considerations, a VR based protocol could improve anxiety outcomes in PD.Clinical implications: VR in PD provides control of a patient's field of view, which can be exploited to induce specific responses, provide visual feedback, analysis of patient actions, and introduce safe challenges in the context of training. VR assisted Cognitive Behavioral Therapy (CBT) tailored to suit subtypes of anxiety disorders in PD have the potential to improve the efficacy and effectiveness of psychotherapy in PD.

The influence of temporal predictability on express visuomotor responses.

Humans are able to generate target-directed visuomotor responses in less than 100 ms after stimulus onset. These "express" responses have been termed stimulus-locked responses (SLRs) and are proposed to be modulated by visuomotor transformations performed subcortically via the superior colliculus. Unfortunately, these responses have proven difficult to detect consistently across individuals. The recent report of an effective paradigm for generating SLRs in 100% of participants appears to change this. The task required the interception of a target moving at a constant velocity that emerged from behind a barrier. Here, we aimed to reproduce the efficacy of this paradigm for eliciting SLRs and to test the hypothesis that its effectiveness derives from the predictability of target onset time as opposed to target motion per se. In one experiment, we recorded surface electromyogram (EMG) from shoulder muscles as participants made reaches to intercept temporally predictable or unpredictable targets. Consistent with our hypothesis, predictably timed targets produced more frequent and stronger SLRs than unpredictably timed targets. In a second experiment, we compared different temporally predictable stimuli and observed that transiently presented targets produced larger and earlier SLRs than sustained moving targets. Our results suggest that target motion is not critical for facilitating the SLR expression and that timing predictability does not rely on extrapolation of a physically plausible motion trajectory. These findings provide support for a mechanism whereby an internal timer, probably located in cerebral cortex, primes the processing of both visual input and motor output within the superior colliculus to produce SLRs.NEW & NOTEWORTHY Express stimulus-driven responses in humans have been proposed to be originated subcortically via the superior colliculus. These short-latency responses are facilitated by the presentation of dynamic visual stimuli. Here, we show that this facilitation is related to the predictable target timing, regardless of its kinematic attributes. We propose that the superior colliculus can be primed to generate express stimulus-driven motor responses via cortical top-down projection.

Trial-by-trial modulation of express visuomotor responses induced by symbolic or barely detectable cues.

Human cerebral cortex can produce visuomotor responses that are modulated by contextual and task-specific constraints. However, the distributed cortical network for visuomotor transformations limits the minimal response time of that pathway. Notably, humans can generate express visuomotor responses in arm muscles that are inflexibly tuned to the target location and occur 80-120 ms from stimulus presentation [stimulus-locked responses (SLRs)]. This suggests a subcortical pathway for visuomotor transformations that might involve the superior colliculus and its downstream reticulo-spinal projections. Here we investigated whether cognitive expectations can modulate the SLR. In one experiment, we recorded surface electromyogram (EMG) from shoulder muscles as participants reached toward a visual target whose location was unpredictable in control conditions and partially predictable in cue conditions by interpreting a symbolic cue (75% validity). Valid symbolic cues led to earlier and larger SLRs than control conditions; invalid symbolic cues produced later and smaller SLRs than control conditions. This is consistent with a cortical top-down modulation of the putative subcortical SLR network. In a second experiment, we presented high-contrast targets in isolation (control) or ∼24 ms after low-contrast stimuli, which could appear at the same (valid cue) or opposite (invalid cue) location as the target and with equal probability (50% cue validity). We observed earlier SLRs than control with the valid low-contrast cues, whereas the invalid cues led to the opposite results. These findings may reflect bottom-up attentional mechanisms, potentially evolving subcortically via the superior colliculus. Overall, our results support both top-down and bottom-up modulations of the putative subcortical SLR network in humans.NEW & NOTEWORTHY Express visuomotor responses in humans appear to reflect subcortical sensorimotor transformation of visual inputs, potentially conveyed via the tecto-reticulo-spinal pathway. Here we show that the express responses are influenced by both symbolic and barely detectable spatial cues about stimulus location. The symbolic cue-induced effects suggest cortical top-down modulation of the putative subcortical visuomotor network. The effects of barely detectable cues may reflect exogenous facilitation mechanisms of the tecto-reticulo-spinal pathway.

VO2peak and 24-hour sleep, sedentary behavior, and physical activity in Australian truck drivers.

This study assessed cardiorespiratory fitness (CRF) and 24-h sleep, sedentary behavior (SB), and physical activity (PA) in Australian truck drivers. Participants (n = 37 men) attended clinic sessions for an exercise test to exhaustion to establish CRF and wore an accelerometer (Actigraph GT3X+) to estimate sleep, SB, and PA. Relative to normative values, CRF was "below percentile 25" in 51% of drivers (mean [SD] VO2peak=30 .1 [7.6] mL.kg-1.min-1). Accelerometer data indicated that total vigorous-intensity (3.5-4.5 min/day) and sustained moderate- to vigorous-intensity PA (>5 min; 0.5-1.6 bouts/day) were limited. The findings show there is a need to design and test PA interventions that can improve poor levels of CRF in truck drivers.

Rapid recalibration of temporal order judgements: Response bias accounts for contradictory results.

Recent history influences subsequent perception, decision-making and motor behaviours. In this article, we address a discrepancy in the effects of recent sensory history on the perceived timing of auditory and visual stimuli. In the synchrony judgement (SJ) task, similar timing relationships in consecutive trials seem more synchronous (i.e. less like the repeated temporal order). This effect is known as rapid recalibration and is consistent with a negative perceptual aftereffect. Interestingly, the opposite is found in the temporal order judgement (TOJ) task (positive rapid recalibration). We aimed to determine whether a simple bias to repeat judgements on consecutive trials (choice-repetition bias) could account for the discrepant results in these tasks. Preliminary simulations and analyses indicated that a choice-repetition bias could produce apparently positive rapid recalibration in the TOJ and not the SJ task. Our first experiment revealed no evidence of rapid recalibration of TOJs, but negative rapid recalibration of associated confidence. This suggests that timing perception was rapidly recalibrated, but that the negative recalibration effect was obfuscated by a positive bias effect. In our second experiment, we experimentally mitigated the choice-repetition bias effect and found negative rapid recalibration of TOJs. We therefore conclude that timing perception is negatively rapidly recalibrated, and this is observed consistently across timing tasks. These results contribute to a growing body of evidence that indicates multisensory perception is constantly undergoing recalibration, such that perceptual synchrony is maintained. This work also demonstrates that participants' task responses reflect judgements that are contaminated by independent biases of perception and decision-making.

When flow is not enough: evidence from a lane changing task.

Humans are able to estimate their heading on the basis of optic flow information and it has been argued that we use flow in this way to guide navigation. Consistent with this idea, several studies have reported good navigation performance in flow fields. However, one criticism of these studies is that they have generally focused on the task of walking or steering towards a target, offering an additional, salient directional cue. Hence, it remains a matter of debate as to whether humans are truly able to control steering in the presence of optic flow alone. In this study, we report a set of maneuvers carried out in flow fields in the absence of a physical target. To do this, we studied the everyday task of lane changing, a commonplace multiphase steering maneuver which can be conceptualized without the need for a target. What is more (and here is the crucial quirk), previous literature has found that in the absence of visual feedback, drivers show a systematic, asymmetric steering response, resulting in a systematic final heading error. If optic flow is sufficient for controlling navigation through our environment, we would expect this asymmetry to disappear whenever optic flow is provided. However, our results show that this asymmetry persisted, even in the presence of a flow field, implying that drivers are unable to use flow to guide normal steering responses in this task.

Incidence of Hospitalization for Stroke in Queensland, Australia: Younger Adults at Risk.

BACKGROUND: Trends in the incidence of stroke are important for health care planning. Information is particularly scarce in Australia, due to the paucity of studies with access to recent, large-scale, longitudinal datasets. In this paper we investigated the incidence of hospitalization for stroke by sex, age, and subtype in the whole State of Queensland (Australia). METHODS: We obtained data of all hospital admissions for stroke in Queensland from 2002 to 2015. Age standardized hospitalization rates for first-ever stroke were calculated along with WHO adjusted rates. Poisson regression analyses were conducted to investigate the influence of time and gender on the incidence of subtypes of stroke as well as the total incidence. RESULTS: Admissions for first-ever stroke were 57,597. Crude hospitalization incidence rose from 87 (95% confidence interval [CI], 84-90) to 108 (95%CI, 105-111) for both sexes. The highest increase was in the age bands 40-49 from 33 (95%CI, 26-40) to 54 (95%CI, 46-62; +62%) and 50-59 from 82 (95%CI, 70-93) to 127 (95%CI, 114-140; +56%) in men and in 60-69 from 118 (95%CI, 100-136) to 159 (95%CI, 143-175; +34%) in women. Ischemic subtype rates appeared to increase more than haemorrhagic rates. Age range, sex, and year reliably predicted incidence rates. CONCLUSIONS: If these trends are maintained, the data predict further increases, especially in males aged 40-59. With people apparently stroking earlier and mortality rates dropping, the healthcare system in Australia is faced with a rapidly increasing care burden.

The face-in-the-crowd effect: Threat detection versus iso-feature suppression and collinear facilitation.

Are people biologically prepared for the rapid detection of threat posed by an angry facial expression, even when it is conveyed in the form of a schematic line drawing? Based on visual search times, the current literature would suggest that the answer is yes. But are there low-level explanations for this effect? Here, we present visual search results for schematic faces using current best practice, based on a concentric search array and set size manipulation. Using this approach, we replicate the classic search advantage for angry over happy faces. However, we also report a comparable effect when abstract plus- and square-shaped stimuli-derived from the angry and happy schematic faces respectively-are used within the same paradigm. We then go on to demonstrate that, while reduced, the effect remains after removal of the circular surround, bringing us closer to the source of the effect. We explore the possibility that the source of this search asymmetry could be the iso-feature suppression and collinear facilitation model proposed in Li's (1999a, 1999b, and 2002) bottom-up model of saliency. Simulations with this model using the abstract stimuli align with the corresponding behavioral results (i.e., the plus shape was found to be more salient than the square). Given the deliberate similarities between these abstract shapes and the respective face stimuli, we propose that the underlying cause for the asymmetries typically found using schematic faces, may be more related to early visual processing of line orientation than threat detection.

Comparison of functional and anatomical estimations of visual acuity in two species of coral reef fish.

The high-contrast, complex patterns typical of many reef fish serve several purposes, including providing disruptive camouflage and a basis for vision-based communication. In trying to understand the role of a specific pattern, it is important to first assess the extent to which an observer can resolve the pattern, itself determined, at least in part, by the observer's visual acuity. Here, we studied the visual acuity of two species of reef fish - Pomacentrus amboinensis and Pseudochromis fuscus - using both anatomical and behavioural estimates. The two species share a common habitat but are members of different trophic levels (predator versus herbivore/omnivore) and perform different visual tasks. On the basis of the anatomical study, we estimated visual acuity to lie between 4.1 and 4.6 cycles deg-1 for P. amboinensis and 3.2 and 3.6 cycles deg-1 for P. fuscus Behavioural acuity estimates were considerably lower, ranging between 1.29 and 1.36 cycles deg-1 for P. amboinensis and 1.61 and 1.71 cycles deg-1 for P. fuscus Our results show that two species from the same habitat have only moderately divergent visual capabilities, despite differences in their general life histories. The difference between anatomical and behavioural estimates is an important finding as the majority of our current knowledge on the resolution capabilities of reef fish comes from anatomical measurements. Our findings suggest that anatomical estimates may represent the highest potential acuity of fish but are not indicative of actual performance, and that there is unlikely to be a simple scaling factor to link the two measures across all fish species.

Assessment of colorectal polyp recognition skill: development and validation of an objective test.

BACKGROUND: The quality of colonoscopy is known to vary. The extent to which colonoscopists can recognize the presence of subtle colorectal lesions by visually distinguishing them from the surrounding mucosa (i.e., polyp recognition skill) may be one of several attributes that influence polyp detection rates. The aim of the present study was to develop and validate the first objective test of polyp recognition skill. METHODS: Validation study. Twenty-eight experienced colonoscopists and eighty novices took a preliminary 280-item computer-based polyp recognition test. Items were genuine endoscopic images which participants assessed for the presence of "likely polyps." Half included clinically identified polyps. Participants clicked on a suspected lesion or a button marked "no likely polyp", and the main outcome measures were accuracy and response latency. The best items were selected for the final 50-item test. RESULTS: In the preliminary test, experienced colonoscopists correctly identified more polyps than novices (P < .0001) and better discriminated between clinically identified polyps and non-polyp features (as measured by d', P < .0001). For polyp items, the experienced group also responded faster (P < .01). Effect sizes were large for accuracy (Cohen's d = 3.22) and d' (Cohen's d = 3.22). The 50 final test items produced comparable results for accuracy, d', and response latency. For both versions of the test, score scale reliability was high for both polyp and non-polyp items (α = .82 to .97). CONCLUSIONS: The observed experienced-novice differences support the construct validity of the performance measures derived from the tests, indicating that polyp recognition skill can be quantified objectively. The final test may potentially be used to assess trainees, but test sensitivity may be insufficient to make fine-grained distinctions between different skill levels among experienced colonoscopists. More sensitive future tests may provide a valuable supplement to clinical detection rates, allowing objective comparisons between skilled colonoscopists.

A novel training device for tip control in colonoscopy: preliminary validation and efficacy as a training tool.

BACKGROUND: Effective control of the colonoscope tip is one of the most fundamental components of colonoscopy skill. Mastering fine tip control can be problematic for novice trainees, yet no validated training regimes exist for developing this specific skill component in isolation. We aimed to conduct a preliminary validation of a novel training device for colonoscopic tip control, and to assess its efficacy as a training tool. METHODS: In study 1 (validation), 13 experienced colonoscopists and 16 novices used a colonoscope to accurately track 28 targets on each of four concave "training surfaces" as quickly as possible, and we compared their performance. In study 2 (pre-post-training study), another 16 novices were tested before and after a six-session training program. In both studies, the main outcome measurements were completion time (measured automatically by the device) and variability of individual performance (the SD of each individual's completion times across trials). RESULTS: Compared with novices, experienced colonoscopists were faster (P < 0.0001) and their performances less variable (P < 0.0001). With training, novices became faster (P < 0.0001) and more consistent (P = 0.003), and these improvements also generalized to novel training surfaces (P's < 0.01). After training, the novices' tip control performance was indistinguishable from that of the experienced colonoscopists (P's > 0.05). The composite measures of completion time used in both studies all had acceptable to excellent internal consistency reliability (α's ranged from 0.72 to 0.93). CONCLUSIONS: We found that performance measures derived from using the device to assess skill can discriminate between experienced colonoscopists and novices in terms of their ability to control and guide the colonoscope tip precisely, providing preliminary evidence to support the construct validity of the metrics. The device is also an effective training tool for this fundamental component of colonoscopy skill.

Assessing colonoscopic inspection skill using a virtual withdrawal simulation: a preliminary validation of performance metrics.

BACKGROUND: The effectiveness of colonoscopy for diagnosing and preventing colon cancer is largely dependent on the ability of endoscopists to fully inspect the colonic mucosa, which they achieve primarily through skilled manipulation of the colonoscope during withdrawal. Performance assessment during live procedures is problematic. However, a virtual withdrawal simulation can help identify and parameterise actions linked to successful inspection, and offer standardised assessments for trainees. METHODS: Eleven experienced endoscopists and 18 endoscopy novices (medical students) completed a mucosal inspection task during three simulated colonoscopic withdrawals. The two groups were compared on 10 performance metrics to preliminarily assess the validity of these measures to describe inspection quality. Four metrics were related to aspects of polyp detection: percentage of polyp markers found; number of polyp markers found per minute; percentage of the mucosal surface illuminated by the colonoscope (≥0.5 s); and percentage of polyp markers illuminated (≥2.5 s) but not identified. A further six metrics described the movement of the colonoscope: withdrawal time; linear distance travelled by the colonoscope tip; total distance travelled by the colonoscope tip; and distance travelled by the colonoscope tip due to movement of the up/down angulation control, movement of the left/right angulation control, and axial shaft rotation. RESULTS: Statistically significant experienced-novice differences were found for 8 of the 10 performance metrics (p's < .005). Compared with novices, experienced endoscopists inspected more of the mucosa and detected more polyp markers, at a faster rate. Despite completing the withdrawals more quickly than the novices, the experienced endoscopists also moved the colonoscope more in terms of linear distance travelled and overall tip movement, with greater use of both the up/down angulation control and axial shaft rotation. However, the groups did not differ in the number of polyp markers visible on the monitor but not identified, or movement of the left/right angulation control. All metrics that yielded significant group differences had adequate to excellent internal consistency reliability (α = .79 to .90). CONCLUSIONS: These systematic differences confirm the potential of the simulated withdrawal task for evaluating inspection skills and strategies. It may be useful for training, and assessment of trainee competence.

When action conditions perception: Evidence of cross-modal cue recruitment.

Goal-directed movement, such as reaching to touch an object, relies heavily on vision. Vision guides our motor system not only during initial targeting but also during online movement correction and error-driven learning. But it is not all one-way traffic. This paper reports a situation in which this perceptual-motor interaction runs in reverse, when action affects concurrent perceptual experience. More to the point, the paper reveals that visual perception is subject to change through learned (even arbitrary) visuomotor associations. By considering a situation in which the perceptual decision is dichotomous, this paper reveals that the brain readily harnesses motor behavior to constrain the formation of a visual percept.

A competency framework for colonoscopy training derived from cognitive task analysis techniques and expert review.

BACKGROUND: Colonoscopy is a difficult cognitive-perceptual-motor task. Designing an appropriate instructional program for such a task requires an understanding of the knowledge, skills and attitudes underpinning the competency required to perform the task. Cognitive task analysis techniques provide an empirical means of deriving this information. METHODS: Video recording and a think-aloud protocol were conducted while 20 experienced endoscopists performed colonoscopy procedures. "Cued-recall" interviews were also carried out post-procedure with nine of the endoscopists. Analysis of the resulting transcripts employed the constant comparative coding method within a grounded theory framework. The resulting draft competency framework was modified after review during semi-structured interviews conducted with six expert endoscopists. RESULTS: The proposed colonoscopy competency framework consists of twenty-seven skill, knowledge and attitude components, grouped into six categories (clinical knowledge; colonoscope handling; situation awareness; heuristics and strategies; clinical reasoning; and intra- and inter-personal). CONCLUSIONS: The colonoscopy competency framework provides a principled basis for the design of a training program, and for the design of formative assessment to gauge progress towards attaining the knowledge, skills and attitudes underpinning the achievement of colonoscopy competence.

Visual acuity in a species of coral reef fish: Rhinecanthus aculeatus.

Coral reef fish present the human observer with an array of bold and contrasting patterns; however, the ability of such fish to perceive these patterns is largely unexamined. To understand this, the visual acuity of these animals - the degree to which they can resolve fine detail - must be ascertained. Behavioural studies are few in number and anatomical analysis has largely focused on estimates of ganglion cell density to predict the visual acuity in coral reef fish. Here, we report visual acuity measures for the triggerfish Rhinecanthus aculeatus. Acuity was first assessed using a series of behavioural paradigms and the figures were then contrasted with those obtained anatomically, based on photoreceptor and ganglion cell counts. Behavioural testing indicated an upper behavioural acuity of 1.75 cycles·degree(-1), which is approximately the same level of acuity as that of the goldfish (Carassiusauratus). Anatomical estimates were then calculated from wholemount analysis of the photoreceptor layer and Nissl staining of cells within the ganglion cell layer. Both of these anatomical measures gave estimates that were substantially larger (7.75 and 3.4 cycles·degree(-1) for the photoreceptor cells and ganglion cells, respectively) than the level of acuity indicated by the behavioural tests. This indicates that in this teleost species spatial resolution is poor compared to humans (30-70 cycles·degree(-1)) and it is also not well indicated by anatomical estimates.

The dynamics of perceptual rivalry in bistable and tristable perception.

Human observers are extremely adept at correctly interpreting the visual input that they receive despite its inherent ambiguity. There are, however, situations in which no single, valid interpretation exists and perception oscillates. Such situations offer insight into the processes underlying perception, as they reveal the conditions under which our percept can alter in the presence of an unchanging physical stimulus. Many studies have focused on perceptual switching during binocular and monocular rivalry, or when viewing ambiguous figures. The majority of these studies have focused on bistable phenomena. In this paper we report the study of a range of ambiguous stimuli that provoke tristable perception, thereby providing a more exacting test bed for current models. We find that subjects spontaneously move from periods of bistable to tristable perception and that this results in a characteristic change in the rate of perceptual switching. In contrast to reports for bistable stimuli, we find only weak evidence for consistency in the relative switch rates of individuals across our test stimuli and explain why our results are inconsistent with the theory of interhemispheric switching. We go on to describe how the results are, instead, largely consistent with models of rivalry based on mutual inhibition and adaptation.