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M Mackeben

Publications and source records attributed to M Mackeben.

11 recordsLinked to original sources
PubMed2001

Rapid, object-based learning in the deployment of transient attention.

We show that transient attention summoned by an exogenous cue shows rapid learning of the relationship between the cue and a subsequent target in a discrimination task. In experiment 1, performance was unaffected when a target always appeared in the same position on a large cue, but was degraded when the target could appear anywhere within the extent of the larger cue. Experiment 2 shows that it was not the predictability of where the target appeared within the cue that aided performance, but rather a consistent location mapping of cue and target, since predictably alternating the target location relative to the cue led to worse performance than when the target was presented in the same location relative to the cue from trial to trial. Further analysis of the results of experiment 2 shows that the learning is rapid, evident after one trial, and has a cumulative influence over four consecutive trials. Possible neural correlates of this form of learning are discussed, with a focus on the supplementary eye fields in the prefrontal cortex. The reported experiments show that transient attention is not a simple reflexive mechanism but can show rapid visuospatial learning, in object-based coordinates.

Association Learning↗
PubMed2000

The importance of sustained attention for patients with maculopathies.

Sustained attention enhances perception in eccentric positions in the visual field, which helps patients with foveal vision loss to develop a peripheral 'preferred retinal locus' (PRL). Besides central scotoma topography, local variations of attentional performance could influence the choice of PRL location. We tested sustained attention augmenting peripheral letter recognition in 23 maculopathy patients and 15 normally-sighted subjects (eight positions, 8 degrees eccentricity). Performance was shown to depend on tested location, which was the same in patients and normals. This indicates that the choice of the PRL location after foveal vision loss can be influenced by topographic features of sustained attention.

Adolescent↗
PubMed1999

Sustained focal attention and peripheral letter recognition.

Topographic characteristics of peripheral letter recognition were investigated using a sustained attention paradigm to clarify whether its deployment in the visual field is equally easy in all eight tested locations at 7.5 deg eccentricity. Target size (36 arcmin) was clearly above threshold, so that letters were easily recognized at long durations (> 500 ms). In the main experiment, they were displayed for an individually determined duration of 66 to 167 ms. Six of twelve normally sighted subjects were in their twenties, the others in their fifties. The target location was cued (1 s), and after 2.5-4 s delay, a target was displayed. The results provide strong evidence that performance depended significantly on location and subject. All spatial characteristics showed anisometry, and most showed vertical asymmetry of either sign. Performance was always best on the horizontal meridian. None of the results correlated with subject age. These findings also show that in disfavored locations, performance is limited by deploying attention there, not by holding it there. Consequently, in low vision rehabilitation after binocular central field loss, the choice of a preferred retinal locus for 'eccentric viewing' can be limited by an attentional factor that is unrelated to the eye disease.

Adolescent↗
PubMed1997

An introduction to accurate display timing for PCs under 'Windows'.

As the use of computers for delivering stimuli in vision research has become ubiquitous, there is an obvious need for accurate timing of display monitors without the use of expensive hardware extensions. If a user should decide to program an application in the increasingly common 'Windows' operating system for IBM PCs and compatibles, a software solution for this problem is not obvious any more. The goal is to achieve display durations down to one single video frame. This article describes several approaches and a tested solution designed to run on any PC or compatible under Windows 3.1/95, regardless of the video card used. This creates new possibilities for low-cost, implementation of visual experiments for laboratory and classroom use.

Computer Terminals↗
PubMed1993

Express attentional shifts.

"Express" saccades, named for their extremely short latencies, occur more frequently in a paradigm with a "gap" in time between the disappearance of the fixation mark and the appearance of the target to be fixated. To explain this result, it has been hypothesized that movements of the eyes are preceded by movements of attention [Posner (1980) Quarterly Journal of Experimental Psychology, 32, 3-25], and that removing the fixation mark allows attention to disengage from the fovea and to be deployed more rapidly to the peripheral target, thus diminishing saccadic latency [Fisher (1987) Reviews of Physiology, Biochemistry and Pharmacology, 105, 1-35]. We measured attention using extra-foveal vernier acuity performance. Our results provide direct evidence supporting the above hypothesis. First, we found that the rise of performance for increasing cue lead times was much faster in the "gap" paradigm. Second, the time function relating gap duration to discrimination performance was remarkably similar to the one relating gap duration and rate of express saccades reported by Mayfrank, Mobashery, Kimmig & Fischer [(1987) European Archives of Psychiatry and Neurological Science, 235, 269-275]. Third, control experiments showed that it was the disappearance of the fixation mark rather than a non-specific warning that led to more rapid shifts of attention and, thus, to better performance. We therefore conclude that the short latencies of "express" saccades may be based on a mechanism involving unusually rapid shifts of attention.

Adult↗
PubMed1989

Sustained and transient components of focal visual attention.

Human observers fixated the center of a search array and were required to discriminate the color of an odd target if it was present. The array consisted of horizontal or vertical black or white bars. In the simple case, only orientation was necessary to define the odd target, whereas in the conjunctive case, both orientation and color were necessary. A cue located at the critical target position was either visible all the time (sustained cuing) or it appeared at a short variable delay before the array presentation (transient cuing). Sustained visual cuing enhanced perception greatly in the conjunctive, but not in the simple condition. Perception of the odd target in the conjunctive display was improved even further by transient cuing, and peak discrimination performance occurred if the cue preceded the target array by 70-150 msec. Longer delays led to a marked downturn in performance. Control experiments indicated that this transient attentional component was independent of the observers' prior knowledge of target position and was not subject to voluntary control. We provide evidence to suggest that the transient component does not originate at the earliest stages of visual processing, since it could not be extended in duration by flickering the cue, nor did it require a local sensory transient to trigger its onset. Neither the variation in retinal eccentricity nor changing the paradigm to a vernier acuity task altered the basic pattern of results. Our findings indicate the existence of a sustained and a transient component of attention, and we hypothesize that of the two, the transient component is operative at an earlier stage of visual cortical processing.

Adolescent↗
PubMed1982

Steady state visual evoked potentials in the alert primate.

Macaque monkeys were trained to fixate a small spot while we recorded epidural steady state visual evoked potentials (SSVEP) in response to counterphase modulated sinusoidal gratings. This led to the following results: (1) the SSVEP can show either broad or narrow spatial frequency tuning, depending on electrode location, temporal frequency, contrast and method of analysis. (2) The SSVEP can also show narrow temporal frequency tuning, as narrow as 0.5 octave at half height. (3) Contrast functions relating VEP amplitude to log contrast were highly nonlinear. We propose that they are the composite of at least two distinct linear functions, one with a shallow slope for low contrasts and one with a significantly steeper slope for the higher contrasts. (4) Extrapolation of the low contrast function to zero voltage can lead to an excellent match with psychophysical functions. A similar extrapolation of the high contrast function, however, leads to a contrast value much higher than the psychophysical threshold. These findings suggest that the SSVEP can reflect the activity of two distinct neural mechanisms responsive to pattern stimulation. The degree to which either mechanism is evident determines the spatial and temporal frequency tuning of the VEP.

Animals↗
PubMed1978

Pursuit eye movements and their neural control in the monkey.

1. Single units in the 3. and 6. nerve nuclei were recorded, together with the stimulus and eye movements in trained macaques during pursuit eye movements. 2. The relationship between the impulse rate of an oculomotor motoneuron and the corresponding eye movements can be described by a first order differential equation only, if distinctions are made between the modes of the oculomotor system (e.g., fixation or pursuit) and between the agonist phase and the antagonist phase of the corresponding eye muscle. 3. The trained monkeys showed a frequency response during pursuit eye movements, which was comparable to that of humans and which clearly indicates the existence of a predictor mechanism. 4. After sudden stimulus disappearance in the pursuit mode, both the neural impulse rate and the eye movement performed smooth changes for more than 1s. These slow post-pursuit eye movements were related to the time course before stimulus disappearance. 5. Our findings lead to the hypothesis, that pursuit eye movements in primates, if elicited by small moving visual stimuli, are generated by means of a feedback system consisting of a predictor mechanism, the parameters of which are continuously corrected by an updating process in the afferent visual system.

Animals↗
PubMed1976

Functional changes in the oculomotor system of the monkey at various stages of barbiturate anesthesia and alertness.

1. Single units in the III. and VI. nerve nuclei were continuously recorded together with vestibular stimuli and eye movements in macaques before, during, and after administration of barbiturate. 2. The visual input was functionally detached from the oculomotor system during the deeper stages of anesthesia, whereas some kind of vestibulo-ocular response could always be elicited. 3. The finding of various phase values between the maximum impulse rate IRmax of oculomotor units and the maximum stimulus velocity vmax during 1 Hz sinusoidal vestibular stimulation ranging from about 65 deg phase lead to 65 deg phase lag is suggested as important for the explanation of the phase shifts between head rotation and eye movement during anesthesia. 4. The phase relationship between IRmax and vmax was found to be unchanged, whereas the characteristic of IRmax versus vmax was highly sensitive to arousal stimuli for some oculomotor neurons. This sensitivity was represented exclusively by activation rather than inhibition.

Anesthesia↗