Biomedical subjects

B Treutwein

Publications and source records attributed to B Treutwein.

9 recordsLinked to original sources

PubMed2001

A system for the assessment and training of temporal-order discrimination.

Two programs were developed for psychophysical assessment and training of temporal-order thresholds in the visual and auditory modalities. Order threshold is defined as the minimum onset interval between two sensory events (stimulus onset asynchrony, SOA) that must exist before an observer is able to indicate the correct order of the events. Brain-injured patients with aphasia and children with language-learning impairments, i.e. those who have been diagnosed as performing poorly on temporal-order tasks and in discriminating stop-consonant vowel syllables, can effectively be trained by a feedback training procedure in which the SOA is manipulated. The performance in the temporal-order task and the ability to discriminate phonemes improves with this procedure. In the diagnostic program, the SOA is changed by an adaptive procedure that generates a sequence of SOAs converging to the threshold and is driven by the responses of the subject. The feedback-training program begins with the presentation of SOAs, which are slightly above the individual order threshold; they are subsequently varied according to the responses of the subject.

Aphasia↗

PubMed2000

Daily rhythm of vigilance assessed by temporal resolution of the visual system.

To assess the daily distribution of temporal resolution in visual detection, binocular double-pulse resolution (DPR) was measured over a 24 h period in six healthy subjects. DPR showed a significant daily variation with an amplitude for the foveal stimulus of up to 60%. Like in other vigilance-dependent daily rhythms, optimal performance occurred around midday. The DPR measurements described here are an excellent method for assessment of vigilance and mental alertness (e.g. in pharmacological studies). They show strong time-of-day differences, are highly reliable across successive measurements, and can be fully automated.

Adult↗

PubMed1999

Fitting the psychometric function.

A constrained generalized maximum likelihood routine for fitting psychometric functions is proposed, which determines optimum values for the complete parameter set--that is, threshold and slope--as well as for guessing and lapsing probability. The constraints are realized by Bayesian prior distributions for each of these parameters. The fit itself results from maximizing the posterior distribution of the parameter values by a multidimensional simplex method. We present results from extensive Monte Carlo simulations by which we can approximate bias and variability of the estimated parameters of simulated psychometric functions. Furthermore, we have tested the routine with data gathered in real sessions of psychophysical experimenting.

Bayes Theorem↗

PubMed1996

Amblyopic quasi-blindness for image structure.

Human amblyopes display reduced contrast sensitivities, suffer from perceptual distortion, and their letter acuities are worse than is predicted from grating visibility. We sought the origin of these dysfunctions by measuring normal and amblyopic sensitivities to various forms of well-defined image distortion, namely band-limited phase quantization, phase quantization with additional amplitude modulation, and grey-scale modification. Our results prove the existence of an amblyopic quasi-blindness to image structure, that cannot be explained in terms of contrast detection. We discuss these findings within the computational scheme of image decomposition into local amplitude and local phase values. they are consistent with the assumption of amblyopic eyes beings impaired in processing local phase but having the local amplitude (or "energy", possibly at reduced gain) at their disposal. Phrased in physiological terms, we propose a scheme of complex-cells-only vision in amblyopia. We also provide a demonstration of how amblyopic eyes may see the test stimuli and natural images by generating local amplitude and phase representations at limited phase resolution.

Amblyopia↗

PubMed1995

Automated perimetry with bright and dark stimuli.

Conventional perimeters use bright stimuli. In this study, dark stimuli were also used. Dark stimuli are employed for testing due to their lack of effects of local scatter and are utilized with the purpose of preferentially stimulating the off-system, but their presentation with optical methods is difficult. This problem is solved by the use of a computer monitor. The objective of this study was to compare directly measurements obtained with bright and dark stimuli. Therefore, the central 30 degrees of the visual field of ten subjects with no ophthalmologic pathology was examined with bright and dark stimuli (size 10- and 30-min-of-arc). Threshold estimation was performed with the 4/2 method. Concerning the 10-min-of-arc dark stimulus, no measurement outside the central 15 degrees could be performed because of insufficient dynamic range (sometimes even the darkest stimulus was not seen). Comparing the results obtained using bright and dark stimuli of the same size, we could not find a significant difference in sensitivity for this age group.

Adaptation, Ocular↗

PubMed1995

Adaptive psychophysical procedures.

Improvements in measuring thresholds, or points on a psychometric function, have advanced the field of psychophysics in the last 30 years. The arrival of laboratory computers allowed the introduction of adaptive procedures, where the presentation of the next stimulus depends on previous responses of the subject. Unfortunately, these procedures present themselves in a bewildering variety, though some of them differ only slightly. Even someone familiar with several methods cannot easily name the differences, or decide which method would be best suited for a particular application. This review tries to illuminate the historical background of adaptive procedures, explain their differences and similarities, and provide criteria for choosing among the various techniques.

Cost-Benefit Analysis↗

PubMed1994

Dissociation of local and global processing in visual agnosia.

Subsequent to strokes in the right and left inferomedial occipito-temporal lobes, two patients became prosopagnosic and alexic, respectively. They also show a complementary dissociation of the analysis of handwritten text. The patient with the right posterior stroke can read it but not recognize whose handwriting it is; the patient with the left posterior stroke cannot read the text but knows who wrote it. The analysis of spatial vision revealed that the prosopagnosic patient has no problem with seeing texture elements when presented in isolation. Yet she performs poorly with Moiré and texture perception, i.e. she suffers from a selective loss of global visual perception. The alexic patient performs well with Moiré patterns but neither with (complex) texture elements nor with textures. She seemingly can locally and globally process patterns composed of simple figural elements but fails with stimuli that require the integration of features. This finding of a concomitant dissociation of local and global visual processes in the two patients supports the view that prosopagnosia as well as alexia are the most conspicuous aspects of more general alterations of visual perception.

Agnosia↗

PubMed1989

Perceptual spatial frequency--orientation surface: psychophysics and line element theory.

We have investigated the discriminability of gratings which simultaneously vary in spatial frequency and orientation. Thirteen and nine reference gratings were used with two observers, and bivariate discrimination probability surfaces were determined around each grating. These data were then fitted to a general bivariate Gaussian function. The results clearly demonstrate local separability in this log frequency and orientation discrimination domain. Our results also show that the factor contributing most to the non-Euclidean nature of such frequency/orientation discrimination is orientation anisotropia, although we also find some evidence for smaller changes in the associated Riemannian line-element at different frequency ranges. These results cast doubt upon claims for a "pseudo line-element" for frequency discrimination based upon the nonlinear outputs of a fixed set of detectors.

Discrimination, Psychological↗

PubMedDate not supplied

Loss of spatial phase relationships in extrafoveal vision.

Objects in peripheral vision are not simply blurred but lack quality of form. Assuming that the visual system performs a (patchwise) Fourier analysis of the retinal image (for review see ref. 2), it has been suggested that this disadvantage of peripheral vision may be due to the inability to encode properly spatial phase relationships. This is of great interest for neurological research as certain visual pathologies imply alterations of perceived form. Previous attempts at measuring phase sensitivities failed to distinguish between the detection of phase-related changes in contrast and phase coding in the visual system. We separated these processing strategies by applying the iso-second-order texture paradigm of Julesz to the discrimination of compound gratings. Our results, reported here, show that the energy detection properties of both foveal and peripheral vision are comparable, however, independently of scale, peripheral vision ignores the relative position of image components.

Fovea Centralis↗