Determination and evaluation of clinically efficient stopping criteria for the multiple auditory steady-state response technique

Background: Although the auditory steady-state response (ASSR) technique utilizes objective statistical detection algorithms to estimate behavioural hearing thresholds, the audiologist still has to decide when to terminate ASSR recordings introducing once more a certain degree of subjectivity. Aims: The present study aimed at establishing clinically efficient stopping criteria for a multiple 80-Hz ASSR system. Methods: In Experiment 1, data of 31 normal hearing subjects were analyzed off-line to propose stopping rules. Consequently, ASSR recordings will be stopped when (1) all 8 responses reach significance and significance can be maintained for 8 consecutive sweeps; (2) the mean noise levels were ≤ 4 nV (if at this “≤ 4-nV” criterion, p-values were between 0.05 and 0.1, measurements were extended only once by 8 sweeps); and (3) a maximum amount of 48 sweeps was attained. In Experiment 2, these stopping criteria were applied on 10 normal hearing and 10 hearing-impaired adults to asses the efficiency. Results: The application of these stopping rules resulted in ASSR threshold values that were comparable to other multiple-ASSR research with normal hearing and hearing-impaired adults. Furthermore, in 80% of the cases, ASSR thresholds could be obtained within a time-frame of 1 hour. Investigating the significant response-amplitudes of the hearing-impaired adults through cumulative curves indicated that probably a higher noise-stop criterion than “≤ 4 nV” can be used. Conclusions: The proposed stopping rules can be used in adults to determine accurate ASSR thresholds within an acceptable time-frame of about 1 hour. However, additional research with infants and adults with varying degrees and configurations of hearing loss is needed to optimize these criteria

Detecting single-trial EEG evoked potential using a wavelet domain linear mixed model: application to error potentials classification

Objective. The main goal of this work is to develop a model for multi-sensor signals such as MEG or EEG signals, that accounts for the inter-trial variability, suitable for corresponding binary classification problems. An important constraint is that the model be simple enough to handle small size and unbalanced datasets, as often encountered in BCI type experiments. Approach. The method involves linear mixed effects statistical model, wavelet transform and spatial filtering, and aims at the characterization of localized discriminant features in multi-sensor signals. After discrete wavelet transform and spatial filtering, a projection onto the relevant wavelet and spatial channels subspaces is used for dimension reduction. The projected signals are then decomposed as the sum of a signal of interest (i.e. discriminant) and background noise, using a very simple Gaussian linear mixed model. Main results. Thanks to the simplicity of the model, the corresponding parameter estimation problem is simplified. Robust estimates of class-covariance matrices are obtained from small sample sizes and an effective Bayes plug-in classifier is derived. The approach is applied to the detection of error potentials in multichannel EEG data, in a very unbalanced situation (detection of rare events). Classification results prove the relevance of the proposed approach in such a context. Significance. The combination of linear mixed model, wavelet transform and spatial filtering for EEG classification is, to the best of our knowledge, an original approach, which is proven to be effective. This paper improves on earlier results on similar problems, and the three main ingredients all play an important role

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

The development of bottom-up and top-down interaction in the processing of goal-directed action

The study of action-cognition is driven by the assumption that what one can do motorically depends on what one can conceive of mentally, given a set of external opportunities (Rosenbaum, Cohen, & Jax, 2007). Therefore, a comprehensive theory of action development ought to integrate perceptual aspects of action processing with conceptual changes that give rise to increasingly abstract behaviours. How and why children progress to higher levels of organization in the processing and coordination of purposeful behaviour is a question that has been at the core of developmental research for decades. Various competences underlying early action processing and decision-making have been identified and linked to sophisticated mental operations later in life. However, considerably less is known about the relationships between perceptual and conceptual abilities and how they interact to shape action development. Goal-pursuit is achieved with increasing efficiency during the preschool period. In fact, by the age of first grade children show substantial abilities to regulate actions into hierarchically structured sequences of events that can be transferred across contexts (e.g., Levy, 1980; Bell & Livesey, 1985; Livesey & Morgan, 1991). The aim of this project was to investigate the perceptual and conceptual processes that drive these remarkable advances as they emerge during the preschool years. The studies in this thesis investigate top-down and bottom-up interactions in the processing of actions at various levels of abstraction. Employing a range of novel paradigms, the results of four studies highlight considerable advances in preschoolers’ abilities to organise actions in terms of goal hierarchies. Findings further highlight that the ability to extract structure at a basic level is readily achieved early in life, while higher-level action comprehension and planning abilities continue to develop throughout the childhood years

Psychophysical responses to earth-vertical rotations in the elderly

A growing elderly population is vulnerable to injury or death due to falls. Previous studies documenting the physiologic changes that occur within the vestibular system due to the aging process have shown moderate decreases in caloric and rotational chair responses. Psychophysical testing, which has proven to be critical to understanding the function of the auditory and other sensory systems, has not yet been used to study vestibular function in the elderly. The present study had two goals: to determine if psychophysical thresholds correlate with performance on standard tests of vestibular function, and to determine if older subjects have poorer vestibular psychophysical thresholds than younger subjects. Eighteen older adults (age range 63-84 years) and thirteen younger adults (age range 20-25 years) participated in the study. Psychophysical testing of vestibular function consisted of rotations about the earth-vertical axis to determine both detection thresholds and discrimination thresholds to angular velocity. Standard tests of vestibular function included sinusoidal harmonic oscillation, steps of velocity, and caloric testing. On average, older adults performed more poorly on psychophysical tests than their younger counterparts. The best older adults did as well as the best younger subjects on both detection and discrimination tasks, but the worst older adults were far poorer than the worst younger subjects. Psychophysical thresholds did not correspond to performance on rotational chair testing. These results demonstrate that normal older adults have a wider performance range than younger subjects on psychophysical testing. It also indicates that psychophysical testing accesses different information than standard tests of vestibular function. This suggests that psychophysical testing may be an important additional method for measuring balance function in the elderly

Eye movements in mild traumatic brain injury: Ocular biomarkers

Mild traumatic brain injury (mTBI, or concussion), results from direct and indirect trauma to the head (i.e. a closed injury of transmitted forces), with or without loss of consciousness. The current method of diagnosis is largely based on symptom assessment and clinical history. There is an urgent need to identify an objective biomarker which can not only detect injury, but inform prognosis and recovery. Ocular motor impairment is argued to be ubiquitous across mTBI subtypes and may serve as a valuable clinical biomarker with the recent advent of more affordable and portable eye tracking technology. Many groups have positively correlated the degree of ocular motor impairment to symptom severity with a minority attempting to validate these findings with diffusion tract imaging and functional MRI. However, numerous methodological issues limit the interpretation of results, preventing any singular ocular biomarker from prevailing. This review will comprehensively describe the anatomical susceptibility, clinical measurement, and current eye tracking literature surrounding saccades, smooth pursuit, vestibulo-ocular reflex, vergence, pupillary light reflex, and accommodation in mTBI