Larger Performance Decrements Research Articles

Spontaneous attentional failures reflect multiplicative interactions of chronic sleep loss with acute sleep loss and circadian misalignment

ObjectivesAcute and chronic sleep loss and circadian timing interact such that, depending on their combination, small or very large performance decrements are observed in tasks of attention. Here, we tested whether such nonlinear interactions extend to a physiological measure of spontaneous visual attentional failures, indicating a fundamental principle of sleep-wake regulation. MethodsNine healthy volunteers completed an in-laboratory 3-week forced desynchrony protocol consisting of 12 consecutive 42.85-hour cycles with a sleep-wake ratio of 1:3.3. The protocol induced increasing chronic sleep loss, while extended wake (32.85 hours) and sleep episodes (10 hours) occurred at multiple circadian phases. Attentional failure rate was quantified from continuous electrooculograms (number of 30-second epochs with slow eye movements/h of wakefulness) as a function of time since scheduled wake (acute sleep loss), week of study (chronic sleep loss), and circadian (melatonin) phase. ResultsDuring the first ∼8 hours awake, attentional failure rate was low, irrespective of the week. During the following wake hours, attentional failure rate increased steadily but at a faster rate in weeks 2 and 3 compared to week 1. The effects of acute and chronic sleep loss on attentional failure rate were magnified during the biological night compared to the biological day. ConclusionsA single extended sleep episode can only temporarily reverse attentional impairment associated with chronic sleep loss. Multiplicative effects of acute and chronic sleep loss—further amplified during the biological night—substantiate the interaction of 2 homeostatic response mechanisms and caution against underestimating their disproportionate combined impact on performance, health, and safety.

Data crowdsourcing on psychomotor and cognitive effects of cannabis via mobile app.

In an effort to educate consumers of cannabis, we created a downloadable application (app) for mobile phones that collects data on the neuropsychological effects related to cannabis use. In particular, the app assessed four domains, these being: (i) psychomotor compensation, (ii) time estimation, (iii) sustained attention, and (iv) response inhibition. These tests were presented as a sequence of video games to be completed in under 10 min. Included in the analysis were 213 users who indicated that they were intoxicated from cannabis at the moment of app use. The control group contained individuals who reported using the app while sober (n = 137). A machine learning model was applied to the data to determine whether a particular pattern of performance was predictive of intoxication, and these results were used to inform the creation of a composite score that reflected aggregate performance for all four (i-iv) video games. Relative to the control group, the largest performance decrements were discovered within the initial 120 min after self-administration. These deficits abated as the time-since-use lengthened, and this pattern was consistent with the time-course of subjectively reported intoxication. Although significant limitations in interpretation exist due to the naturalistic and self-report data collection method, this proof-of-concept study points toward the potential utility of mobile app detection of cannabis effect. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Interactions between the aging brain and motor task complexity across the lifespan: balancing brain activity resource demand and supply.

The Compensation Related Utilization of Neural Circuits Hypothesis (CRUNCH) proposes a framework for understanding task-related brain activity changes as a function of healthy aging and task complexity. Specifically, it affords the following predictions: (i) all adult age groups display more brain activation with increases in task complexity, (ii) older adults show more brain activation compared with younger adults at low task complexity levels, and (iii) disproportionately increase brain activation with increased task complexity, but (iv) show smaller (or no) increases in brain activation at the highest complexity levels. To test these hypotheses, performance on a bimanual tracking task at 4 complexity levels and associated brain activation were assessed in 3 age groups (20-40, 40-60, and 60-80years, n = 99). All age groups showed decreased tracking accuracy and increased brain activation with increased task complexity, with larger performance decrements and activation increases in the older age groups. Older adults exhibited increased brain activation at a lower complexity level, but not the predicted failure to further increase brain activity at the highest complexity level. We conclude that older adults show more brain activation than younger adults and preserve the capacity to deploy increased neural resources as a function of task demand.

On the role of different subdimensions of inhibition for successful motor skill change.

Modifying already automatized movement skills often causes proactive interference resulting in initial performance decrements. Dealing with interference is closely linked to inhibitory functions, since inhibition is needed to suppress automatic, but undesired behavior. The aim of this study was to investigate the role of three different inhibition dimensions for interference control in motor skill change. To this end, 42 participants performed three tests each measuring a different dimension of inhibition: resistance to distractor interference (Eriksen-Flanker Task), resistance to proactive interference (Brown-Peterson Variant) and prepotent response inhibition (Stop-Signal Task). To examine the amount of proactive interference in a motor skill change task, participants were then asked to type a short paragraph as fast and accurately as possible on a regular computer keyboard. After this baseline measure, in order to induce proactive interference, they were confronted with a manipulated keyboard on which the letters S and L were switched. This change led to an immediate performance decline, observable in increased typing times and errors. Results also showed that larger performance decrements were significantly associated with better baseline performance, lower scores on prepotent response inhibition and higher scores on resistance to distractor interference. Besides supporting the idea of inhibition as a multidimensional construct, these findings replicate and confirm recent research indicating that the success in motor skill change is predicted by the ability to suppress prepotent response tendencies.

Neurophysiological correlates of age differences in driving behavior during concurrent subtask performance

Driving is a complex cognitive-motor task that requires the continuous integration of multisensory information, cognitive processes, and motor actions. With higher age, driving becomes increasingly challenging as a result of naturally declining neurophysiological resources. Performing additional subtasks, such as conversations with passengers or interactions with in-vehicle devices (e.g., adjusting the radio), may further challenge neurocognitive resources that are required to maintain driving performance. Based on declining brain physiological resources and inferior neurocognitive functioning, older adults (OA) may show higher brain activation and larger performance decrements than younger adults (YA) when engaging in additional subtasks during driving. Age differences, however, may further vary for different neurocognitive task demands, such that driving performance of OA might be particularly affected by certain subtasks. In this study, we hence investigated the brain functional correlates of age differences in driving behavior during concurrent subtask performance in YA and OA. Our final sample consisted of thirty younger (21.80 ± 1.73y, 15 female) and thirty older (69.43 ± 3.30y, 12 female) regular drivers that drove along a typical rural road (25 - 30 min) in a driving simulator and performed three different concurrent subtasks that were presented auditorily or visually: typing a 3-digit number (TYPE), comparing traffic news and gas station prices (working memory, WM), and stating arguments (ARG). We measured variability in lateral car position, velocity, and following distance to a frontal lead car as the standard deviation from 0 to 15 s after subtask onset. Brain activity was continuously recorded using functional near-infrared spectroscopy over the dorsolateral prefrontal cortex. Both YA and OA particularly varied in their lateral position during TYPE with a more pronounced effect in OA. For YA, in contrast, ARG led to higher variability in velocity compared to TYPE and WM, whereas OA showed no task-specific differences. Substantiating our behavioral findings, OA revealed the largest brain functional response to TYPE, while YA demonstrated a very distinct activation during ARG and smaller hemodynamic responses to TYPE and WM. Brain activity in the DLPFC was, overall, not significantly, but small to moderately related to certain behavioral performance parameters (mainly lateral position). We conclude that both OA and YA are vulnerable to distractive subtasks while driving. Age differences, however, seem to largely depend on neurocognitive task demands. OA may be at higher risk for accidents when performing visuo-motor subtasks (e.g., interacting with navigational systems) during driving while YA may be more (cognitively) distracted when talking to passengers.

Hearing-Impaired Listeners Show Reduced Attention to High-Frequency Information in the Presence of Low-Frequency Information.

Many listeners with sensorineural hearing loss have uneven hearing sensitivity across frequencies. This study addressed whether this uneven hearing loss leads to a biasing of attention to different frequency regions. Normal-hearing (NH) and hearing-impaired (HI) listeners performed a pattern discrimination task at two distant center frequencies (CFs): 750 and 3500 Hz. The patterns were sequences of pure tones in which each successive tonal element was randomly selected from one of two possible frequencies surrounding a CF. The stimuli were presented at equal sensation levels to ensure equal audibility. In addition, the frequency separation of the tonal elements within a pattern was adjusted for each listener so that equal pattern discrimination performance was obtained for each CF in quiet. After these adjustments, the pattern discrimination task was performed under conditions in which independent patterns were presented at both CFs simultaneously. The listeners were instructed to attend to the low or high CF before the stimulus (assessing selective attention to frequency with instruction) or after the stimulus (divided attention, assessing inherent frequency biases). NH listeners demonstrated approximately equal performance decrements (re: quiet) between the two CFs. HI listeners demonstrated much larger performance decrements at the 3500 Hz CF than at the 750 Hz CF in combined-presentation conditions for both selective and divided attention conditions, indicating a low-frequency attentional bias that is apparently not under subject control. Surprisingly, the magnitude of this frequency bias was not related to the degree of asymmetry in thresholds at the two CFs.

The Effect of Personal Protective Equipment on Firefighter Occupational Performance

PURPOSE: To determine the effect of load carriage (LC) and the self-contained breathing apparatus (SCBA) on occupational performance of structural firefighters. METHODS: Twenty-one professional male structural firefighter recruits (Age: 28.6 ± 4.3 yr; Height:178.6 ± 7.2 cm; Body mass: 94.1 ± 15.4 kg; Body fat: 17.8 ± 8.4%) participated in the study. Occupational physical ability was assessed by time to complete a simulated fire ground test (SFGT). The SFGT was composed of a stair climb, charged hose drag, equipment carry, ladder raise, forcible entry, search, and victim rescue. Subjects performed 2 familiarization trials and 3 trials of a SFGT in different conditions: physical training clothes only (PT), wearing turnout gear and an SCBA (but not breathing through the SCBA (LC)), and wearing turnout gear and breathing through the SCBA (SCBA). RPE was also measured. Heart rate, blood lactate, and perceived exertion were assessed during the SFGT. Repeated measures ANOVAs were used to identify differences among trials. To describe within group changes, relative difference scores were calculated as follows: % difference = (([experimental trial outcome – PT outcome]/ PT outcome) x 100). RESULTS: The SCBA trial took 44.5 ± 15.5% longer (345.9 ± 43.7s; p<.001) and the LC trial took 38.3 ± 12.6% longer (331.2 ± 39.3s; p<.001) than the PT trial (241.0 ± 33.3s). The SCBA trial took longer than the LC trial (p = .046). Heart rate and lactate measures were not different between trials. RPE was higher in the SCBA trial (6.7 ± 1.7) and LC (6.3 ± 1.5) compared to the PT trial (4.6 ± 1.8; p<.001). CONCLUSION: Load carriage and the respirator elicit a large decrement in occupational performance. Performance in PT clothes is not an accurate depiction of performance in load carriage. Firefighters and practitioners must identify safe and effective training strategies to prepare firefighters for the occupational demands of load carriage and respirator use.

Effects of Altitude/Hypoxia on Single- and Multiple-Sprint Performance: A Comprehensive Review.

Many sport competitions, typically involving the completion of single- (e.g. track-and-field or track cycling events) and multiple-sprint exercises (e.g. team and racquet sports, cycling races), are staged at terrestrial altitudes ranging from 1000 to 2500m. Our aim was to comprehensively review the current knowledge on the responses to either acute or chronic altitude exposure relevant to single and multiple sprints. Performance of a single sprint is generally not negatively affected by acute exposure to simulated altitude (i.e. normobaric hypoxia) because an enhanced anaerobic energy release compensates for the reduced aerobic adenosine triphosphate production. Conversely, the reduction in air density in terrestrial altitude (i.e. hypobaric hypoxia) leads to an improved sprinting performance when aerodynamic drag is a limiting factor. With the repetition of maximal efforts, however, repeated-sprint ability is more altered (i.e. with earlier and larger performance decrements) at high altitudes (>3000-3600m or inspired fraction of oxygen <14.4-13.3%) compared with either normoxia or low-to-moderate altitudes (<3000m or inspired fraction of oxygen >14.4%). Traditionally, altitude training camps involve chronic exposure to low-to-moderate terrestrial altitudes (<3000m or inspired fraction of oxygen >14.4%) for inducing haematological adaptations. However, beneficial effects on sprint performance after such altitude interventions are still debated. Recently, innovative 'live low-train high' methods, in isolation or in combination with hypoxic residence, have emerged with the belief that up-regulated non-haematological peripheral adaptations may further improve performance of multiple sprints compared with similar normoxic interventions.

Effects of acute alcohol consumption on measures of simulated driving: A systematic review and meta-analysis

Driving simulators are used in a wide range of research settings to help develop an understanding of driver behavior in complex environments. Acute alcohol impairment is an important research topic for traffic safety and a large number of studies have indicated levels of simulated driving impairment imposed by alcohol across a range of performance outcome variables. The aim of the present study was to examine the impact of acute alcohol consumption on simulated driving performance by conducting a systematic review and meta-analysis of the available evidence. The online databases PubMed (MEDLINE), Web of Science (via Thomas Reuters) and Scopus were searched to identify studies that measured simulated car driving performance under control ('no alcohol' or ‘placebo alcohol’ ingestion) and intervention (acute alcohol ingestion) conditions, using repeated-measures experimental designs. Primary research outcomes were standard deviation of lane position (SDLP) and standard deviation of speed (SDSP); (total number of lane crossings (LC) and average speed (Speed) were secondary research outcomes). Meta-analytic procedures were used to quantify the effect of acute alcohol consumption on vehicle control, and to determine the influence of methodological variables (i.e. the duration of the simulated driving task, the limb of the BAC curve (ascending vs. descending) and the type of driving simulator employed (i.e. car vs. PC-based)) on the magnitude of the performance change due to alcohol consumption. 423 records were screened, and 50 repeated-measures trials (n=962 participants, 62% male) derived from 17 original publications were reviewed. 37 trials (n=721 participants) used a ‘placebo alcohol’ comparator to determine the effect of alcohol consumption on SDLP (32/37) and SDSP (22/37). Alcohol consumption significantly increased SDLP by 4.0±0.5cm (95% CI: 3.0, 5.1) and SDSP by 0.38±0.10km⋅h−1 (95% CI: 0.19, 0.57). Regression analyses indicate BAC (p=0.004) and driving simulator platform (p<0.001) influence the magnitude of the SDLP change, such that higher BAC levels and the use of PC-based driving simulators were associated with larger performance decrements (R2=0.80). The limb of the BAC curve and the duration of the driving task did not significantly alter the magnitude of the performance change. Eleven trials (n=205 participants) used a ‘no alcohol’ comparator to measure the effect of alcohol consumption on SDLP (10/11); few trials assessed SDSP (3/11). Alcohol consumption resulted in a small significant increase in SDLP under these conditions (standardized difference in means=0.23, 95% CI: 0.06, 0.39). These results demonstrate that lateral (SDLP and LC) and longitudinal (SDSP) vehicle control measures in a driving simulator are impaired with acute alcohol consumption. However, SDLP appears to be a more sensitive indicator of driving impairment than other driving performance variables and the results of the present study support its use as a performance outcome when examining alcohol-induced simulated driving impairment.

Word Memory Test Performance Across Cognitive Domains, Psychiatric Presentations, and Mild Traumatic Brain Injury.

The current study addressed two aims: (i) determine how Word Memory Test (WMT) performance relates to test performance across numerous cognitive domains and (ii) evaluate how current psychiatric disorders or mild traumatic brain injury (mTBI) history affects performance on the WMT after excluding participants with poor symptom validity. Participants were 235 Iraq and Afghanistan-era veterans (Mage = 35.5) who completed a comprehensive neuropsychological battery. Participants were divided into two groups based on WMT performance (Pass = 193, Fail = 42). Tests were grouped into cognitive domains and an average z-score was calculated for each domain. Significant differences were found between those who passed and those who failed the WMT on the memory, attention, executive function, and motor output domain z-scores. WMT failure was associated with a larger performance decrement in the memory domain than the sensation or visuospatial-construction domains. Participants with a current psychiatric diagnosis or mTBI history were significantly more likely to fail the WMT, even after removing participants with poor symptom validity. Results suggest that the WMT is most appropriate for assessing validity in the domains of attention, executive function, motor output and memory, with little relationship to performance in domains of sensation or visuospatial-construction. Comprehensive cognitive batteries would benefit from inclusion of additional performance validity tests in these domains. Additionally, symptom validity did not explain higher rates of WMT failure in individuals with a current psychiatric diagnosis or mTBI history. Further research is needed to better understand how these conditions may affect WMT performance.

Sprint performance under heat stress: A review.

Training and competition in major track-and-field events, and for many team or racquet sports, often require the completion of maximal sprints in hot (>30 °C) ambient conditions. Enhanced short-term (<30 s) power output or single-sprint performance, resulting from transient heat exposure (muscle temperature rise), can be attributed to improved muscle contractility. Under heat stress, elevations in skin/core temperatures are associated with increased cardiovascular and metabolic loads in addition to decreasing voluntary muscle activation; there is also compelling evidence to suggest that large performance decrements occur when repeated-sprint exercise (consisting of brief recovery periods between sprints, usually <60 s) is performed in hot compared with cool conditions. Conversely, poorer intermittent-sprint performance (recovery periods long enough to allow near complete recovery, usually 60-300 s) in hotter conditions is solely observed when exercise induces marked hyperthermia (core temperature >39 °C). Here we also discuss strategies (heat acclimatization, precooling, hydration strategies) employed by "sprint" athletes to mitigate the negative influence of higher environmental temperatures.

Caudate Volume Predicts Neurocognitive Performance in Youth with Heavy Prenatal Alcohol Exposure

Fetal alcohol spectrum disorders result from heavy prenatal alcohol exposure and are characterized, in some cases, by central nervous system anomalies and cognitive impairment. Regional patterns of neuroanatomical abnormalities suggest that alcohol exerts selective damage on the developing fetal brain. This study assessed brain-behavior relationships in a sample of youth with histories of heavy prenatal alcohol exposure. The aim was to characterize how structural brain alterations observed in our previous studies relate to cognitive deficits commonly reported in individuals with histories of heavy prenatal alcohol exposure. Twenty-one youth (mean age 13years) with histories of heavy prenatal alcohol exposure and 7 nonexposed healthy comparison subjects underwent structural magnetic resonance imaging and neurobehavioral testing. Regional brain volumes within the alcohol-exposed group were correlated with neuropsychological measures of cognitive control and verbal learning/recall, as these aspects of cognition have previously been shown to be vulnerable to alcohol teratogenesis. Between-group effect sizes revealed moderate to large cognitive performance and brain volume decrements in alcohol-exposed subjects, compared with typically developing peers. Within the alcohol-exposed group, volume of the caudate nuclei was the most consistent predictor of neuropsychological performance, after controlling for potentially confounding variables including total brain volume, IQ, and age. These data are consistent with previous research associating gestational alcohol exposure with structural and functional changes of the caudate nucleus. Our findings extend this previous work by demonstrating that volume reductions of the caudate have behavioral relevance for this population, in relation to cognitive control and verbal learning and recall abilities.

Visuo-perceptual organization and working memory in patients with schizophrenia

We explore the mechanisms sub-tending the re-organization and memorization of visual information by studying how these mechanisms fail in patients with schizophrenia. Several studies have suggested that patients have difficulties in organizing information in perception and memory. We explore to what extent prompting patients to group items influences memory performance. We distinguish automatic grouping from top-down grouping processes, which are especially involved in re-organizing information. The main task was to memorize pairs of figures. Following manipulation of proximity, pairs of figures were part of the same perceptual group (within-group pair, formed on the basis of automatic grouping) or belonged to different groups (between-group pairs, re-grouped through top-down processes). Prior to the memory task, subjects ran a perception task prompting them to prioritize either within-group or between-group pairs. Unlike patients, controls globally benefited from grouping by proximity in the memory task. In addition, the results showed that prioritizing between-group pairs had a deleterious effect in patients, but with a large decrement in memory performance in the case of within-group rather than between-group figures. This occurred despite preserved focalization on within-group figures, as shown by eye-movement recordings. The suggestion is that when patients are prompted to re-group separate items, they can do so, but the benefit derived from automatic grouping is then not only lost but also reversed. This suggests re-organizing visual information not only involves re-grouping separate items but also integrating these new groups in a unified representation, which is impaired in patients with schizophrenia.

Relationships Between Repeated Sprint Testing, Speed, and Endurance

Repeated sprint testing is gaining popularity in team sports, but the methods of data analysis and relationships to speed and endurance qualities are not well described. We compared three different methods for analyzing repeated sprint test results, and we quantified relationships between repeated sprints, short sprints, and endurance test scores. Well-trained male junior Australian Football players (n = 60, age 18.1 +/- 0.4 years, height 1.88 +/- 0.07 m, mass 82.0 +/- 8.1 kg; mean +/- SD) completed a 6 x 30-m repeated sprint running test on a 20-second cycle, a 20-m sprint test (short sprint), and the 20-m multistage shuttle run for endurance. Repeated sprint results were evaluated in three ways: total time for all six sprints (TOTAL), percent change from predicted times (PRED) from the fastest 30-m sprint time, and percent change from first to last sprint (CHANGE). We observed a very large decrement (CHANGE 6.3 +/- 0.7%, mean +/- 90% confidence limits) in 30-m performance from the first to last sprint (4.16 +/- 0.10 to 4.42 +/- 0.11 seconds, mean +/- SD). Results from TOTAL were highly correlated with 20-m sprint and 20-m multistage shuttle run tests. Performance decrements calculated by PRED were highly correlated with TOTAL (r = 0.91), but neither method was directly comparable with CHANGE (r = -0.23 and r = 0.12 respectively). TOTAL was moderately correlated with fastest 20-m sprint time (r = 0.66) but not the 20-m multistage shuttle run (r = -0.20). Evaluation of repeated sprint testing is sensitive to the method of data analysis employed. The total sprint time and indices of the relative decrement in performance are not directly interchangeable. Repeated sprint ability seems more related to short sprint qualities than endurance fitness.

Sequence learning and selection difficulty.

The authors studied the role of attention as a selection mechanism in implicit learning by examining the effect on primary sequence learning of performing a demanding target-selection task. Participants were trained on probabilistic sequences in a novel version of the serial reaction time (SRT) task, with dual- and triple-stimulus participants having to ignore irrelevant items in the SRT display. Despite large performance decrements under dual- and triple-stimulus configurations, testing under single-stimulus conditions revealed no impairment to sequence learning. These findings suggest that implicit sequence learning is resistant to disruption of the selection process. Results are discussed in terms of a componential model of attention and in relation to the implicit-explicit distinction.

Adaptive Task Prioritization in Aging: Selective Resource Allocation to Postural Control Is Preserved in Alzheimer Disease

With age, the performance of multiple tasks decreases, a pattern exaggerated in Alzheimer disease (AD). At the same time, recent research, based on adaptive theories of healthy aging, indicates a preference of older adults to allocate resources toward tasks of higher immediate value (e.g., postural control). This study investigated whether such models also hold for pathologic cognitive aging. Using a dual-task paradigm, the authors combined a working memory with a postural control task under easy and difficult conditions in patients with AD, older adults, older adults low on performance on a cognitive marker test, and young adults (N = 40). Participants repeatedly performed a cognitive and a postural control task both simultaneously and in isolation over the course of eight sessions. Consistent with earlier studies on divided attention in age and AD, the authors found large dual-task performance decrements with age and more so in AD. When not challenged, patients with AD showed large performance decrements under dual-task conditions in both postural control and working memory. With increasing difficulty in the postural control task, however, older adults, and more so patients with AD, maintained a high level of functioning in postural control, as compared with working memory. The findings indicate that the theory of selective optimization with compensation extends to pathologic aging and have broad implications for models of dual-task performance and executive control in aging and AD.

Cognitive Requirements for Vestibular and Ocular Motor Processing in Healthy Adults and Patients with Unilateral Vestibular Lesions

This study investigated the role of cognition in the vestibulo-ocular reflex (VOR) and ocular pursuit using a dual-task paradigm in patients with unilateral peripheral vestibular loss and healthy adults. We hypothesized that cognitive resources are involved in successful processing and integration of vestibular and ocular motor sensory information, and this requirement would be greater in patients with vestibular dysfunction. Sixteen well-compensated patients with surgically confirmed absent unilateral peripheral vestibular function and 16 healthy age- and sex-matched controls underwent seven combinations of vestibular-only, visual-only, and visual-vestibular stimuli while performing three different information processing tasks. Visual-vestibular stimuli included a semicircular canal and an otolith stimulus provided through seated chair rotations; fixation on a laser target and sinusoidal smooth pursuit while still; and fixation on a head-fixed laser target during chair rotations. The information processing tasks were three different auditory reaction time (RT) tasks: (1) simple RT, (2) disjunctive RT, and (3) choice RT. Our results showed increases in RTs in both patients and controls under all vestibular-only stimulation conditions and during ocular pursuit. Patients showed greater increases in RTs during vestibular stimulation and the more complex disjunctive and choice RT tasks. No differences between the groups were found during the visual-only or visual-vestibular interaction conditions. These results reveal interference between vestibulo-ocular processing and a concurrent RT task, suggesting that the VOR and the ocular motor system are dependent upon cognitive resources to some extent, and thus, are not fully automatic systems. We speculate that this interference with cognition occurs as a result of the sensory integration required for resolving inputs from multiple sensory streams. The particularly large decrement in information processing task performance of the patients compared with controls during vestibular stimulation suggests that compensation for unilateral vestibular loss requires continued cognitive resources.

Reference-frame misalignment and cardinal direction judgments: group differences and strategies.

In 3 experiments, the authors examined how misalignment of egocentric and exocentric reference frames affects cardinal direction judgments. Experiments 1 and 2 demonstrated large differences in the accuracy and speed with which 104 less experienced and 7 experienced navigators made cardinal direction judgments. Reference-frame misalignment was associated with large performance decrements. The extent of these decrements diminished as ability and experience increased: however, even experienced navigators showed decrements when reference frames were misaligned. In Experiment 3, the authors used 55 college students to examine the individual subtasks of a common strategy for cardinal direction judgments and to isolate the effects of reference-frame misalignment to a particular subtask of this strategy. The tasks and strategies studied in this article can be applied in the development of navigational training and interfaces.

Timing of Discrete Actions: Evidence for Perceptual Dominance in Human Performance

An experiment involving a street-crossing task is described. The subjects were required to release a pedestrian within a narrow window of opportunity to cross the road without being run over by vehicles. To test a number of hypotheses on whether timing of actions is driven by perceptual cues or some internal clocking mechanisms, the experiment involved conditions where the street-crossing task was either visible throughout trials or where the vehicles were removed, and coupled with a concurrent mental arithmetic loading task with either visually or auditorily presented stimuli The data support the hypothesis that when the stimuli remain visible, people predominantly rely on perceptual cues for timing discrete actions. Significant performance decrements were observed in the removal conditions Importance of the visual component in the task performance was supported by the larger performance decrement in the unmasked condition when the subjects' attention had to be divided between two sets of visual stimuli. When the primary task stimuli were removed, the clock counting seems to be the preferred strategy for the task under study.

Frequency discrimination in budgerigars (Melopsittacus undulatus): effects of tone duration and tonal context.

Studies of frequency resolving power in budgerigars (Melopsittacus undulatus) have shown that this species has excellent discrimination abilities for both simple and complex sounds falling in the region of 2 to 4 kHz--the frequency range of their contact call. In four experiments, frequency discrimination by budgerigars of short tones similar to elements found in the contact call was examined. Frequency difference limens (FDLs) for simple pure tones at 2.86 kHz were constant for tone durations above 20 ms but higher for shorter tones. Budgerigars generally showed larger FDLs for shorter duration 1-, 2-, and 4-kHz pure tones. FDLs in budgerigars for 20-ms tones embedded in a sequence of six other tones were similar to FDLs measured for tones of the same frequency presented in isolation. Moreover, there was no effect of introducing trial-by-trial variation in the location of the frequency change in the seven-tone complexes for budgerigars, a condition for which humans showed a large decrement in performance. Taken together, these results suggest budgerigars possess enhanced spectral resolving power for short duration pure tones when they are embedded in contact call-like tonal patterns.