Saccadic eye movement related scalp potentials--scalp distribution of presaccadic slow negative potential

This study compared the effects of various rotary instruments and polishing agents on tooth enamel. Topographical features of enamel were studied at consecutive stages of polishing with photoanalysis of scanning electron micrographs. The results indicate that enamel modified by diamond burs may be polished to produce the smoothest surface with white finishing stones, Ceramist finishing points, and flour of pumice.     

The aftereffect of tracking eye movements

When observers tracked moving stripes across a background either of stationary stripes, or of stripes moving in the opposite direction, they saw a clear motion aftereffect when the stripes stopped moving. The direction of this aftereffect was opposite to that of the previously tracked stripes, and was thus the same as the direction of the retinal movement of the non-tracked stripes. This aftereffect of tracking was shown not to depend upon slippage of the tracked contours on the retina during tracking, or upon the saccadic phase of optokinetic nystagmus. The effect showed storage over a period of time with the eyes shut. It appears that the effect is due to induced movement, and arises originally from stimulation of the retina by background contours in the tracking phase. This was shown by confining the view of the moving target to one eye, while permitting both eyes to be exposed to background stimulation during tracking. After such stimulation the magnitude of the aftereffect was equal in the two eyes.     

Principles underlying real-time nystagmus analysis of horizontal and vertical eye movements recorded with electro-, infra-red-, or video-oculographic techniques

We evaluated a means of training special education teachers in supervisory strategies for improving specific teaching-related performances of their paraprofessional, teacher assistants. Using classroom-based instruction and on-the-job monitoring and feedback, seven teachers were trained to systematically observe the data collection and teaching performances of their assistants as well as to provide contingent feedback. The supervisory training for teachers, evaluated using a multiple-probe design across groups of assistants, was accompanied by improvements in data collection performances among seven of eight assistants. Improvement in other teaching skill applications also occurred. The improved performance among the assistants was maintained across a 17-month follow-up period. The supervisory training seemed to have multiple benefits in that the teachers' own teaching-related performances improved once teachers were trained to systematically observe and provide feedback to their assistants. The need for continued research is discussed to evaluate the benefits of supervisory training to improve and maintain other important areas of staff performance.     

The guidance of eye movements during active visual search

An analysis of monkey eye movements in classic conjunction and feature search tasks was made. The task was to find and fixate a target in an array of stimuli. Saccades targeted stimuli accurately (red and green bars, 1.25 x 0.25 degrees), landing most of the time within 1.0 degree of the stimulus center and rarely in blank areas far from any stimulus. Monkeys used target color, but not orientation, to selectively guide search. Saccades moved the point of fixation on the average just beyond the area that could be examined by focal attentive mechanisms during the current fixation, as described in a previous paper (Motter BC, Belky EJ. The zone of focal attention during active visual search. Vis Res 1998;38:1007-22). This distance scales with the density of relevant stimuli in the scene. The saccade targeting data suggest that the locations of items of a particular color, but apparently not of a particular orientation, are available outside the region of focal attention. Color feature selection can apparently block the distracting effects of color unique distractors during search.     

The relationship between visual attention and eye movements.

Experimental psychologists have recently amassed a great deal of evidence supporting the hypothesis that the visual system can select a particular location over other locations in the visual field for further analysis without overtly orienting the eyes to the selected location. At the same time, we know that during reading and scene perception, the eyes are overtly directed to new regions of the visual field every 200 to 300 msec on average. How are covert shifts of attention and overt movements of the eyes related during complex visual-cognitive tasks? The available evidence from studies of the perceptual span in reading suggests that attention is allocated asymmetrically around the fixation point, with more information acquired in the direction that the eyes are moving. Based on this evidence and evidence from explorations of eye movement control in reading, the author presents a tentative model of the relationship between attention and eye movements, called the Sequential Attention Model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The processing of metonymy: Evidence from eye movements.

The authors investigated the time course of the processing of metonymic expressions in comparison with literal ones in 2 eye-tracking experiments. Experiment 1 considered the processing of sentences containing place-for-institution metonymies such as the convent in That blasphemous woman had to answer to the convent; it was found that such expressions were of similar difficulty to sentences containing literal interpretations of the same expressions. In contrast, expressions without a relevant metonymic interpretation caused immediate difficulty. Experiment 2 found similar results for place-for-event metonymies such as A lot of Americans protested during Vietnam, except that the difficulty with expressions without a relevant metonymic interpretation was somewhat delayed. The authors argue that these findings are incompatible with models of figurative language processing in which either the literal sense is accessed first or the figurative sense is accessed first. Instead, they support an account in which both senses can be accessed immediately, perhaps through a single under specified representation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of voluntary eye movements on associations and mood

OBJECTIVE: Our aim was to compare the outcome of esophageal resection for carcinoma in elderly patients (aged over 70 and over 80 years) with that of younger patients managed within a single specialist thoracic surgery unit. PATIENTS AND METHODS: Between January 1987 and November 1997, 523 patients underwent esophagectomy for carcinoma in the Nottingham City Hospital Thoracic Surgery Unit. The patients were divided into 3 groups by age: group I, under 70 years (n = 337); group II, 70 to 79 years (n = 150), and group III, 80 to 86 years (n = 36). These groups were compared with regard to preoperative medical status, operability and resectability, complications, operative mortality, and longterm survival. RESULTS: Patients in groups II (6.0%) and III (2.8%) had fewer preexisting respiratory problems than patients in group I (12.5%), and the patients in group III had fewer preexisting cardiovascular problems (16.7%) than patients in groups I (25.2%) and II (32.7 %). Although patients in group III were generally less likely to have operable lesions (64.3%), no significant differences in resectability rate were detected among the 3 groups (80.8%, 77.7%, and 80%). Elderly patients (groups II and III) had a higher incidence of overall (34% and 36.1%), respiratory (24.7% and 19.4%), and cardiovascular (7.3% and 11.1%) complications than those aged under 70 years (24.6%, 16.3%, and 2.1%, respectively). However, operative mortality (4.7%, 6.7%, and 5.6%) and 5-year survivals inclusive of operative mortality (25.1%, 21.2%, and 19.8%) were similar among the 3 groups. CONCLUSIONS: Accumulated experience in all aspects of perioperative management may account for a low hospital mortality in elderly patients despite a greater operative risk. The survival benefit is similar to that in the younger age groups, enforcing the view that esophagectomy within specialist thoracic units can be safely offered (in appropriately selected patients) with acceptable long-term survival in all age groups.     

The role of eye movements in subitizing and counting.

Previous work has suggested that eye movements may be necessary for accurate enumeration beyond the subitization range of about 4 items. This study determined the frequency of eye movements normally made during enumeration, their relationship to response times, and whether they are required for accurate performance. This was achieved by monitoring eye movements and comparing performance when observers were allowed to saccade and when they were not. The results showed that (a) there was a sharp increase in saccadic frequency beyond about 4 items (from = 0.2 saccades per item to about 1 per item), and (b) enumeration of fewer than 4 items remained rapid and accurate even when eye movements were prevented, whereas enumeration beyond this became less efficient and sometimes less accurate. The results are discussed in relation to the memory and processing requirements of enumeration tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The word grouping hypothesis and eye movements during reading.

The distribution of landing positions and durations of first fixations in a region containing a noun preceded by either an article (e.g., the soldiers) or a high-frequency 3-letter word (e.g., all soldiers) were compared. Although there were fewer first fixations on the blank space between the high-frequency 3-letter word and the noun than on the surrounding letters (and the fixations on the blank space were shorter), this pattern did not occur when the noun was preceded by an article. R. Radach (1996) inferred from a similar experiment that did not manipulate the type of short word that 2 words could be processed as a perceptual unit during reading when the first word is a short word. As this different pattern of fixations is restricted to article-noun pairs, it indicates that word grouping does not occur purely on the basis of word length during reading; moreover, as the authors demonstrate, one can explain the observed patterns in both conditions more parsimoniously without adopting a word-grouping mechanism in eye movement control during reading. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Photoelectric methods of recording eye movements.

Presents 2 photoelectric methods of recording eye movements to investigate the oculomotor system of hospitalized patients with local brain lesions. The general appearance, operation, and advantages of (a) recording horizontal eye movements with direct ink-writing registration, and (b) simultaneous recording of horizontal and vertical eye movements are described. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adaptive modification of saccadic eye movements.

Experiments are reported in which the target for a saccadic eye movement was displaced during the saccade. Ss adapted to the displacement by altering the amplitudes of subsequent saccades to compensate for it. Analysis of kinematic details of the saccade trajectories revealed that the adaptation did not arise from a simple remapping of perceived target locations. Instead, the adaptation appeared to be accomplished by a change in the gain of the saccadic system. The gain change arose primarily from a change in the magnitude of the force pulse for the saccade, not a change in the duration of the pulse. These results have implications for the mechanisms that underlie saccades in normal situations. In particular, people can separately adjust the magnitudes and durations of the force pulses used to produce saccades. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Radial optic flow induces vergence eye movements with ultra-short latencies

An observer moving forwards through the environment experiences a radial pattern of image motion on each retina. Such patterns of optic flow are a potential source of information about the observer's rate of progress, direction of heading and time to reach objects that lie ahead. As the viewing distance changes there must be changes in the vergence angle between the two eyes so that both foveas remain aligned on the object of interest in the scene ahead. Here we show that radial optic flow can elicit appropriately directed (horizontal) vergence eye movements with ultra-short latencies (roughly 80 ms) in human subjects. Centrifugal flow, signalling forwards motion, increases the vergence angle, whereas centripetal flow decreases the vergence angle. These vergence eye movements are still evident when the observer's view of the flow pattern is restricted to the temporal hemifield of one eye, indicating that these responses do not result from anisotropies in motion processing but from a mechanism that senses the radial pattern of flow. We hypothesize that flow-induced vergence is but one of a family of rapid ocular reflexes, mediated by the medial superior temporal cortex, compensating for translational disturbance of the observer.     

Lexical control of within-word eye movements.

Eye movements were recorded during the reading of long words, which were presented in isolation at their optimal viewing position. Refixations were found to be preferentially directed toward the region of the word that contained the critical letters for distinguishing it from its competitors. In Experiments 1 and 2, low-frequency stimulus words sharing all letters except the initial ones with a high-frequency stimulus word (critical letters at the beginning of the word) elicited more left refixations than low-frequency stimulus words sharing all letters except the final ones with a high-frequency stimulus word (critical letters at the end of the word). A similar result was found in Experiments 3 and 4, using an orthographic priming paradigm. These results suggest that refixations are linked to the selection stage of lexical access, aimed at isolating a single lexical entry among a set of candidates activated during the first fixation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Estimate of physiological variability of peak latency in single sweep P300

Lengthening is generally accepted method of treatment for extremity length discrepancy. This attractive method carries the risk of many complications that may ruin primary treatment plan. The aim of this paper was to analyze complications and their management in own material consisting of 60 extremities in 58 patients aged 8-37 years. Limb length discrepancy was caused by congenital bony hypoplasia in 44 cases, trauma in 8 and infection in 8 cases. Initial shortening ranged from 4 to 15 cm (mean 6.5 cm). Ilizarov technique was used in 20 cases, Wagner method in 6 cases and DeBastiani in 34 cases. Expected elongation has been achieved in 60% cases; in remaining 40% complications occurred. New bone formation disturbances and axial malalignement were among most severe ones. An autogenic marrow injections were used to stimulate callus formation, osteogenon was administered. Axial malalignement was corrected by osteotomy. Percentage of complications decreased as number of elongations performed increased.     

Recent studies of eye movements in reading.

Grouping the studies under the general topic headings of techniques of measurement, analysis of the reading process, training to improve eye movements, typography and eye movements, and eye movements and fatigue the author reviews the relevant research literature which has appeared since January, 1945. In general there has been a dimunition of interest in this area. However, there has appeared a large amount of work on visual fixation, speed of eye movements, reaction time of the eye, oculomotor efficiency, and vision during eye movements. There is a need for more basic research. 72-item bibliography. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The presaccadic cortical negativity prior to self-paced saccades with and without visual guidance

The presaccadic negativity (PSN) of the scalp EEG potential prior to self-initiated saccades aimed either at a visual target or at the remembered position of that target in total darkness was analysed in 10 normal subjects. Under both conditions a PSN with a negligible EOG contamination was found, showing 4 characteristics: (1) In both conditions, the PSN maximum is localized at the vertex, probably containing the activity of the supplementary motor area. (2) At an electrode placed over the frontal eye field (FEF) contralateral to the saccade direction, there is a temporary, circumscribed maximum prior to saccades to the visual target, thus probably reflecting activity of the FEF. (3) Prior to saccades to the visual target, there is a statistically significant interhemispheric difference of the PSN over the parietal cortex with a larger amplitude over the hemisphere contralateral to the saccade direction; this might be attributed to directed visual attention. (4) Prior to saccades without visual guidance in darkness there is a statistically significant interhemispheric difference of the PSN over the frontal cortex with a larger amplitude over the hemisphere contralateral to the saccade direction. The amplitude of the PSN decreased in the course of the experiment, probably due to psychological factors such as attention and motivation. Our results suggest that the PSN is a readiness potential preceding voluntary saccades, containing activity related both to unspecific psychological processes and to specific movement preparation in the frontal and parietal ocular motor areas.     

The effect of a moving distractor on the initiation of smooth-pursuit eye movements

As a step toward understanding the mechanism by which targets are selected for smooth-pursuit eye movements, we examined the behavior of the pursuit system when monkeys were presented with two discrete moving visual targets. Two rhesus monkeys were trained to select a small moving target identified by its color in the presence of a moving distractor of another color. Smooth-pursuit eye movements were quantified in terms of the latency of the eye movement and the initial eye acceleration profile. We have previously shown that the latency of smooth pursuit, which is normally around 100 ms, can be extended to 150 ms or shortened to 85 ms depending on whether there is a distractor moving in the opposite or same direction, respectively, relative to the direction of the target. We have now measured this effect for a 360 deg range of distractor directions, and distractor speeds of 5-45 deg/s. We have also examined the effect of varying the spatial separation and temporal asynchrony between target and distractor. The results indicate that the effect of the distractor on the latency of pursuit depends on its direction of motion, and its spatial and temporal proximity to the target, but depends very little on the speed of the distractor. Furthermore, under the conditions of these experiments, the direction of the eye movement that is emitted in response to two competing moving stimuli is not a vectorial combination of the stimulus motions, but is solely determined by the direction of the target. The results are consistent with a competitive model for smooth-pursuit target selection and suggest that the competition takes place at a stage of the pursuit pathway that is between visual-motion processing and motor-response preparation.     

The relationship between curvature and velocity in two-dimensional smooth pursuit eye movements

Curvature and tangential velocity of voluntary hand movements are constrained by an empirical relation known as the Two-Thirds Power Law. It has been argued that the law reflects the working of central control mechanisms, but it is not known whether these mechanisms are specific to the hand or shared also by other types of movement. Three experiments tested whether the power law applies to the smooth pursuit movements of the eye, which are controlled by distinct neural motor structures and a peculiar set of muscles. The first experiment showed that smooth pursuit of elliptic targets with various curvature-velocity relationships was most accurate when targets were compatible with the Two-Thirds Power Law. Tracking errors in all other cases reflected the fact that, irrespective of target kinematics, eye movements tended to comply with the law. Using only compatible targets, the second experiment demonstrated that kinematics per se cannot account for the pattern of pursuit errors. The third experiment showed that two-dimensional performance cannot be fully predicted on the basis of the performance observed when the horizontal and vertical components of the targets used in the first condition were tracked separately. We conclude that the Two-Thirds Power Law, in its various manifestations, reflects neural mechanisms common to otherwise distinct control modules.     

The effects of semantic consistency on eye movements during complex scene viewing.

Eye movements were recorded while participants viewed line-drawing pictures of natural scenes in preparation for a memory test (Experiment 1) or to find a target object (Experiment 2). Initial saccades in a scene were not controlled by semantic information in the visual periphery, although fixation densities and fixation durations were affected by semantic consistency. The results are compared with earlier eye-tracking studies, and a qualitative model of eye movement control in scene perception is discussed in which initial saccades in a scene are controlled by visual but not semantic analysis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)