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PubMed2001

Central auditory processing of durational changes in complex speech patterns by newborns: an event-related brain potential study.

In this study, newborns' ability to discriminate durational changes in the fricative /s/ within a nonsense word was investigated. The results showed that infrequent increments and decrements of a speech sound duration elicit a mismatch negativity kind of response in sleeping human newborns. In the auditory event-related potential to these deviant stimuli two negative waves of this response were revealed. The first negative wave peaked at about 150 msec and the second at about 350 msec after the change onset. At least one negative deflection, which was interpreted as evidence for stimulus change-detection, was observed in every infant.

Adult↗
PubMed1990

Spatiotemporal contrast sensitivity differs in normal aging and Parkinson's disease.

We measured contrast sensitivity for static and laterally drifting vertical gratings in 12 young adults, 7 normal elderly adults, and 8 patients with Parkinson's disease (PD). We compared static and motion contrast sensitivity for spatial frequencies of 0.25, 1, and 4 cycles per degree (cpd), and temporal frequencies of 1, 3, and 9 Hz. Results show that normal aging leads to a reduction of motion sensitivity for the spatial frequency of 0.25 cpd. Compared with elderly controls, PD patients do not present specific abnormalities in this domain. However, for spatial frequencies of 1 and 4 cpd and temporal frequencies of 1 and 3 Hz, motion sensitivity is worse than static sensitivity in PD patients and not in elderly controls. These findings suggest a specific deficit of motion perception in PD, and possible dopaminergic involvement in the control of visuospatial behavior.

Adult↗
PubMed2000

When will the ball rebound? Evidence for the usefulness of mental analogues in appraising the duration of motions.

This study explores the way people appraise the duration of motions when these are only seen momentarily. Three possible theoretical accounts of this skill were developed. The first and second held an analogy between the duration of motions and their visuospatial representations. The third account was based on the existence of a pure chronometrical representation. Three copies of a tennis ball trajectory were created to reproduce the characteristics of the trajectory in terms of each account. The participants first memorized the copy and then used it to appraise the duration of the actual ball trajectory seen only momentarily at the beginning of its flight. The performance of a group given the visuospatial copy paralleled those of a referent group who were allowed to see the actual referent trajectory to memorize its duration. Results showed the importance of visuospatial analogous representations. However, a spatial representation seems to allow better memorization of motion duration.

Adult↗
PubMed1999

Temporal detection in human vision: dependence on spatial frequency.

In the study of perception of temporal changes in luminance, it is customary to model perceptual performance as based on one or more linear filters. The task is then to estimate the temporal impulse responses or the representation of the impulse response in the frequency domain. Previously, temporal masking data have been used to estimate the properties and numbers of these temporal mechanisms (filters) in central vision for 1-cycle-per-degree (cpd) targets [Vision Res. 38, 1023 (1998)]. The same methods have been used to explore how properties of the estimated filters change with stimulus contrast energy [J. Opt. Soc. Am. A 14, 2557 (1997)]. We present estimated properties for temporal mechanisms that detect low spatial-frequency patterns. The results indicate that two filters provide the best model for performance when mask contrast is significant. There are also differences between properties for mechanisms that detect signal spatial frequencies of 1 cpd and 1/3 cpd. The sensitivity of the low-pass mechanism relative to the bandpass mechanism is reduced at 1/3 cpd, consistent with previous findings.

Artifacts↗
PubMed2000

Spatiotemporal filters in the detection of background modulation targets.

The background modulation method has been proposed as a useful test of early visual mechanisms [Biol. Cybern. 37, 77 (1980); Biol. Cybern. 47, 173 (1983)]. The task involves measuring detection thresholds for a luminous spot (increment) drifting over a spatially or temporally modulated background. The study explores the nature of the detecting mechanism in terms of spatial and temporal filters for both spatial and temporal background modulations. In both cases we find that thresholds can be explained by spatial contrast cues generated by the moving spot and that their spatiotemporal characteristics suggest detection by magnocellular processes.

Adult↗
PubMed2001

Perception of spatiotemporal random fractals: an extension of colorimetric methods to the study of dynamic texture.

Recent work establishes that static and dynamic natural images have fractal-like l/falpha spatiotemporal spectra. Artifical textures, with randomized phase spectra, and 1/falpha amplitude spectra are also used in studies of texture and noise perception. Influenced by colorimetric principles and motivated by the ubiquity of 1/falpha spatial and temporal image spectra, we treat the spatial and temporal frequency exponents as the dimensions characterizing a dynamic texture space, and we characterize two key attributes of this space, the spatiotemporal appearance map and the spatiotemporal discrimination function (a map of MacAdam-like just-noticeable-difference contours).

Colorimetry↗
PubMed2002

Adaptation of spatiotemporal mechanisms by increment and decrement stimuli.

Sawtooth modulation has been used in the past to examine visual sensitivity to luminance increments and decrements. The threshold elevation caused by adaptation depends on the spatial profile of the stimulus field and the polarities of the adaptation and test stimuli. We hypothesized that the adaptation effects reflect a change in the sensitivity of the spatiotemporal channels that detect the stimuli. We used a 2-deg disk centered in a larger surround field. Five levels of contrast between the test field and surround were investigated: equiluminant, three intermediate levels, and dark. At each contrast, observers adapted for 5 s to 2-Hz sawtooth modulation (rapid-on or rapid-off). Immediately after adaptation, thresholds were measured for detection of a single cycle of either a rapid-on or a rapid-off waveform. Varying the contrast of the surround affected observers' sensitivity to the polarity of the sawtooth stimulus to the extent that the pattern of sensitivity with the equiluminant surround was the opposite of that with the dark surround. To examine temporal factors, we measured thresholds for slow (500-ms ramps) and fast (8.3-ms pulses) test stimuli. The adaptation effect was preserved with the ramp stimuli but not with the pulse stimuli. Blurring the edge between the test and surround fields in the equiluminant surround condition raised thresholds for all sawtooth test stimuli, suggesting that spatiotemporal channels sensitive to high spatial frequencies and low temporal frequencies facilitate detection in that condition. These findings suggest that adaptation to sawtooth modulation can differentially effect the sensitivity of ON and OFF pathways, but the relative desensitization of each pathway depends on an interaction with the adaptation state of spatiotemporal channels that are involved in detection.

Adaptation, Physiological↗
PubMed1985

Receptive-field symmetry probed using converging gratings.

Contrast-sensitivity functions (CSF's) for converging and diverging gratings were obtained under voluntary fixation at several field widths and under retinal stabilization at one field width. In general, these types of gratings had similar CSF's at all temporal frequencies tested, a result that can be explained by plausible spatiotemporal receptive-field models possessing spatial antisymmetry but not by models possessing pure (even) spatial symmetry. Phase condition at the central line in converging and diverging gratings affected grating detectability at high spatial frequencies, as expected.

Differential Threshold↗
PubMed1986

Determining the kinematic parameters of a moving imaging sensor by processing spatial and temporal intensity changes.

A method is presented that determines the motion parameters of an imaging sensor by evaluating the spatial and temporal intensity changes in the image plane. It is not necessary to compute the optical flow. If the environment in the field of view is described parametrically, constraint equations between the kinematic parameters and the intensity changes can be derived. Linear solutions of these equations are the so-called pure parameters, which are nonlinear functions of the motion parameters. These quantities are the roll, pitch, and yaw rate, the angle of attack and the angle of yaw, and orientation parameters. They can be obtained directly by solving a 3 X 3 eigenvalue problem. The algorithm was implemented and applied to artificial and natural image sequences. An error and covariances analysis shows that the method is robust and accurate enough for autonomous navigation.

Algorithms↗
PubMed1988

Spatial-frequency tuning as a function of temporal frequency and stimulus motion.

Spatial-frequency tuning at two different spatial frequencies was determined by measuring the detectability of a signal grating that was made difficult to see by low- or high-pass visual noise. The signals were vertical sinusoidal gratings of different spatial frequencies. The detectability of the signal was measured in two-alternative forced-choice tasks with different temporal envelopes: (1) a slowly changing raised-cosine (Hanning) window, (2) a rectangularly gated 2-Hz counterphase flickering envelope, and (3) a rectangularly gated 10-Hz counterphase flickering envelope. Additional measurements were made using drifting stimuli with the signal and noise drifting in the same or in opposite directions. The temporal envelopes were chosen because they have different effects on the contrast-sensitivity function and it was desired to know how temporal factors affect the spatial-frequency tuning of the relatively narrowly tuned channels thought to underlie contrast sensitivity. The results show that, for counterphase flickering stimuli, spatial-frequency tuning does not depend on temporal envelopes applied identically to the signal and to the masking noise. A similar picture emerges at slow (2.7-deg/sec) but not at fast (10.9-deg/sec) drift rates.

Contrast Sensitivity↗
PubMed2004

A behavioral assessment of hippocampal function based on a subregional analysis.

The purpose of this review is to determine whether specific subregions (dentate gyrus [DG], CA3, and CA1) of the hippocampus provide unique contributions to specific processes associated with intrinsic information processing exemplified by novelty detection, encoding, pattern separation, pattern association, pattern completion, retrieval, short-term memory and intermediate-term memory. Based on anatomical neural network organization, electrophysiology of cellular activity, lesions, early gene activation, and computational modeling, it can be shown that there exists extensive cooperation among the three subregions of the hippocampus, but there also exists reliable specificity of function for each of the subregions of the hippocampus. The primary process supported by the DG subregion of the hippocampus can be characterized by orthogonalization of sensory inputs to create a metric spatial representation. Furthermore the DG participates in conjunction with CA3 in supporting spatial pattern separation. The CA3 subregion of the hippocampus supports processes associated with spatial pattern association, spatial pattern completion, novelty detection, and short-term memory. The CA1 subregion of the hippocampus supports processes associated with temporal pattern association, temporal pattern completion, and intermediate-term memory. Furthermore, the CA3 in conjunction with CA1 supports temporal pattern separation. All the above-mentioned processes are assumed to reflect intrinsic processing of information within the hippocampus. The diversity of functions associated with the different subregions of the hippocampus suggests that one should not treat the hippocampus as a single entity, but rather that one should concentrate on elucidating further the functions of both dorsal and ventral subregions of the hippocampus and pathways that directly connect each of the subregions as well as their connections with the entorhinal cortex.

Animals↗
PubMed1999

Measuring quality of life in paediatric patients.

The purpose of this paper is to highlight important considerations in the measurement of health-related quality of life (HR-QOL) in paediatric populations. Considerations specific to the evaluation of HR-QOL in children include children's understanding of the questions being asked, their understanding of their own disease, using parents as proxies, time perception problems and simply the fact that children are continually changing. We provide a review of the currently available literature regarding paediatric HR-QOL assessments to examine the different instruments and approaches taken to assess HR-QOL in paediatrics. Asthma-specific measures are discussed as examples of condition-specific HR-QOL instruments because of the considerable amount of methodological and developmental work that has been conducted in this disease. Our search strategy revealed 15 main generic and 5 main asthma-specific instruments that met our criteria for inclusion. The main points high-lighted for each instrument are the description of domains, respondent (i.e. the child, parent or clinician), age group, number of items, format of instrument (usually self-administered or by interview), original country and language, and the existence of translations. For the various studies in which the different instruments are used, the issues of patient population tested, sample size, reliability and validity are addressed. Although this paper does not attempt to be an exhaustive study of paediatric HR-QOL instruments, we provide an overview of the main generic and asthma-specific instruments, as well as an examination of the different methods used in assessing paediatric HR-QOL. Many challenges exist in the measurement of HR-QOL in paediatric patients. With increased attention to the considerations high-lighted, the field will continue to grow, and the usefulness and application of HR-QOL measures in paediatric patients is likely to improve.

Child↗