Fixation Shifts Research Articles

Does auditory attention shift in the direction of an upcoming saccade?

In a series of experiments, we examined whether auditory attention shifts in the direction of an upcoming saccade, as recently reported for visual attention. Normal listeners made speeded discriminations for the elevation (up versus down) of abrupt sounds, regardless of their laterality. Each sound was presented around the time that a lateral saccade was made. Auditory elevation discriminations were reliably faster when the saccade was made towards the side of the auditory probe rather than away. Furthermore, an auditory probe on one side speeded up centrally-cued saccades made in that direction, although sounds did not influence saccades to peripheral visual events. The latter visual events were insufficient to affect hearing unless a saccade was made towards them. A further study showed that fixating towards or away from sounds, rather than saccading, could also affect elevation judgements, with poorer performance when fixating away. However, the influence of an upcoming saccade upon hearing could not be reduced to this fixation effect, since the saccade influence was found even for sounds which terminated before any shift in fixation began. Taken together, our results imply that the direction of an upcoming saccade can affect hearing, as can eye-position.

Visual function and perinatal focal cerebral infarction.

To evaluate the visual function of infants with perinatal cerebral infarction in whom the site and size of the lesion has been determined using magnetic resonance imaging (MRI). Twelve infants with cerebral infarction on MRI were studied with a battery of tests specifically designed to evaluate visual function in infancy. This included tests: for visual attention (fixation shifts); of cerebral asymmetry (optokinetic nystagmus, visual fields); for assessment of acuity (forced choice preferential looking); and neurophysiological measures of vision (phase reversal and orientation reversal visual evoked potential). A considerable incidence of abnormalities on at least one of the tests for visual function used was observed. The presence or severity of visual abnormalities could not always be predicted by the site and extent of the lesion seen on imaging. Early focal lesions affecting the visual pathway can, to some extent, be compensated for by the immature developing brain. These data suggest that all the infants presenting with focal lesions need to be investigated with a detailed assessment of various aspects of vision.

Macular Sparing as a Perimetric Artifact

Purpose We studied the hypothesis that the typical macular sparing of a few degrees was based on an unstable fixation coupled with a nystagmiform searching movement in the direction of the seeing hemiretina. Methods By means of microperimetry with a scanning laser ophthalmoscope, we recently tested the visual fields of 15 hemianoptic patients, through direct visual control of the retina. The tests provided us with accurate information about all fixation shifts that occurred. Results Twelve patients showed macular sparing of 1 to 5 degrees both in the Goldmann visual field and in the scanning laser ophthalmoscope field. Their fixation shifted regularly 1 to 10 degrees toward the seeing hemiretina one to two times per second, then returned rapidly to the foveola. Conversely, three patients showed greater macular sparing, and they all had particular characteristics—extensive fixation shifts, dual fixation, and limited quadrantanopsia. Conclusions We believe that macular sparing could be interpreted as a perimetric (not an anatomic) artifact, provided that the results of these tests on 15 patients are confirmed by further similar studies.

Age-related change and stability of individual differences in infant saccade reaction time

Several facets of continuity in infant information processing were studied longitudinally using the visual expectation paradigm in a sample of 24 infants. At both 4 and 6 months of age, infants viewed an identical left-right alternating sequence of pictures while their eye movements were recorded. Human observers coded the videotape records to document saccadic reaction times (RT), rates of anticipatory fixation shifts to future pictures, and off-task behaviors. Measures of RT were reliable within each assessment and showed strong stability of individual differences across sessions. Measures of anticipation and off-task behaviors revealed few age differences, some within-session reliability, but no stability across sessions. Results provide strong evidence for continuity in some component of infant information processing during the early months of life.

The effect of red and neutral density filters on the degree of eccentric fixation

The reported shift of fixation to a more central position when a red filter is placed before an eye which fixates eccentrically, has never been satisfactorily explained. To further investigate this phenomenon, 14 subjects with eccentric fixation were recruited. A Wratten No. 92 filter was placed before the eccentrically fixating eye, and any change of fixation was assessed by the after-image transfer test. A neutral density (ND) filter was then used, to mimic the reduced retinal illumination caused by the red filter. The results suggest that there is a significant reduction in the eccentricity of fixation, when placing the red filter before an eccentrically fixating eye, and also when placing the ND filter. No significant difference in the effects produced by either filter was found. This suggests that it is the reduction in retinal illuminance caused by the red filter which contributes towards such improvements in fixation.

The effect of red and neutral density filters on the degree of eccentric fixation

The reported shift of fixation to a more central position when a red filter is placed before an eye which fixates eccentrically, has never been satisfactorily explained. To further investigate this phenomenon, 14 subjects with eccentric fixation were recruited. A Wratten No. 92 filter was placed before the eccentrically fixating eye, and any change of fixation was assessed by the after-image transfer test. A neutral density (ND) filter was then used, to mimic the reduced retinal illumination caused by the red filter. The results suggest that there is a significant reduction in the eccentricity of fixation, when placing the red filter before an eccentrically fixating eye, and also when placing the ND filter. No significant difference in the effects produced by either filter was found. This suggests that it is the reduction in retinal illuminance caused by the red filter which contributes towards such improvements in fixation.

Macular Sparing as a Perimetric Artifact

We studied the hypothesis that the typical macular sparing of a few degrees was based on an unstable fixation coupled with a nystagmiform searching movement in the direction of the seeing hemiretina. By means of microperimetry with a scanning laser ophthalmoscope, we recently tested the visual fields of 15 hemianoptic patients, through direct visual control of the retina. The tests provided us with accurate information about all fixation shifts that occurred. Twelve patients showed macular sparing of 1 to 5 degrees both in the Goldmann visual field and in the scanning laser ophthalmoscope field. Their fixation shifted regularly 1 to 10 degrees toward the seeing hemiretina one to two times per second, then returned rapidly to the foveola. Conversely, three patients showed greater macular sparing, and they all had particular characteristics--extensive fixation shifts, dual fixation, and limited quadrantanopsia. We believe that macular sparing could be interpreted as a perimetric (not an anatomic) artifact, provided that the results of these tests on 15 patients are confirmed by further similar studies.

Fixation and central visual field after perifoveal krypton laser treatment of subfoveal neovascularizations.

In contrast to focal laser treatment of large subfoveal neovascular membranes, perifoveal laser treatment sparing the central avascular zone can partially retain central macular function in some cases. The anatomical and functional outcome of this technique was analysed in 26 patients with large subfoveal neovascular membranes (0.6 to 3.0 disc diameter) secondary to age-related macular degeneration (24 cases) or presumed ocular histoplasmosis syndrome (two cases). Patients were followed for six to 39 months. Out of 26 patients 21 had a stable dry scar at the last follow-up examination. Central fixation was retained postoperatively in nine out of 13 patients with central fixation prior to laser treatment. Visual acuity was maintained or improved in 19 out of 26 treated eyes. Statpack analysis (Humphrey Field Analyser) of the long-term results of patients with central fixation indicated an increase in the depth of their relative central scotoma not only immediately after laser treatment but also in the first and second postoperative years. This increasing depth of central scotoma subsequently led to a shift of central fixation to a paracentral area in four out of nine patients six to nine months after treatment. Indocyanine-green angiography showed remaining subfoveal choroidal vasculature corresponding to the area of central fixation, as found in fundus microperimetry by scanning laser ophthalmoscope. Perifoveal laser treatment seems to be effective in maintaining some initial macular function for a limited time in selected patients suffering from subfoveal neovascular membranes.

Central Visual Field, Visual Acuity, and Sudden Visual Loss After Glaucoma Surgery

The relationship between Snellen visual acuity and central visual field loss as determined by the Humphrey 10-degree test was examined in 96 glaucomatous eyes of 79 patients. The severity of the field defect was determined by the number of affected quadrants, defined as a sensitivity loss of at least 10 decibels from normal at the most central point of 1.4-degree eccentricity. The decrease in median acuity was gradual, one-half line per quadrant for one and two affected quadrants, and an additional one and one-half line to two lines for three and four quadrants. Loss of acuity was disproportionate when both temporal quadrants were affected. The major source of error was difficulty with fixation. One type, a prolonged fixation shift, was not related to short-term fixation losses. There was a significant correlation between acuity and foveal threshold over a wide range of both variables. Sudden visual loss from additional optic nerve damage was studied retrospectively in 96 eyes with advanced glaucoma and a central field defect. A frequency of 3% for any loss of visual acuity and a frequency of 1% for a loss to 20/200 or worse were noted. There were no apparent predictive factors.

Sensory Visual Loss And Cognitive Deficits In The Selective Attentional System Of Normal Infants And Neurologically Impaired Children

The ability of infants to shift their gaze laterally from a central target (fixation shift) was investigated in normal one- and three-month-old infants in two visual tasks; competition (central fixating stimulus remained visible while peripheral target was presented) and non-competition (central fixating stimulus replaced by peripheral target). The younger infants were significantly more disrupted by the competition condition, in terms of latency to refixate and direction of first eye movement. An immature attention system is proposed to explain this affect. In addition, visually evoked potentials in response to comparable stimuli were easier to elicit in older infants, suggesting that the one-month-olds possessed more immature sensory and perceptual visual systems, as well as poorer neural systems for controlling selective attention. Both techniques have been applied to a group of neurologically impaired children, and the results indicate that the tests may be useful in distinguishing sensory loss from attentional impairments in these patients.

Search performance without eye movements

Visual search performance (with sets chosen to elicit both serial and parallel search patterns) under two conditions that precluded saccades was compared to the typical situation in which visual inspection of the array is possible. In one condition, the display duration was so brief that any saccades that were executed would be too late to bring the targeted portion of the array into the fovea. In the other, the display remained present until the subject's response, but eye position was monitored and trials with shifts in fixation were excluded from analysis. The latter condition produced search latencies that were nearly identical to those with free inspection. Brief exposure, in contrast, did not produce the pattern typical of serial search, presumably because of strategies induced to deal with the rapid decay of the visual array. It is concluded that saccadic eye movements play little role in the patterns of performance used to infer serial and parallel search, and that brief exposure is not a satisfactory technique for exploring the role of saccadic eye movements in visual search.

Sse of photosynthetic parameters for the diagnosis of copper deficiency in Pinus radiata seedlings

Six‐month‐old water cultures of Pinus radiataI D. Don seedlings showed optimal growth, and the highest CO2 assimilation and photosystem I‐dependent ascorbate/dichlorophenolindophenol → NADP+ electron flow, at 3.0 uM Cu2+ (excess) in the hydroponic media. In the nine‐month‐old water cultures, when the early Cu deprivation has been overcome, the optimum for plant growth and CO2 fixation shifts to 0.3 uM Cu2+ (normal); at that time, the 3.0 uM Cu2+ water cultures showed toxic symptoms of foliar chlorosis. Under Cu2+ deficient levels (0.03 uM) a clear decrease in the photosystem I‐linked electron transport and CO2 assimilation rates, as well as in the whole plant development, could be observed. Both six‐ and nine‐month‐old water cultures showed a close relationship between the Cu2+ concentration of the media and the foliar Cu content. However, leaf chlorophyll and the Cu content of thylakoid lamellae showed such a correlation only in the Cu2+ deficient and Cu2+ normal water cultures. The conclusion from these results is that the electron transport rate ascorbate/dicblorophenolindophenol → NADP+, and the Cu content of the photosynthetic membranes, can be used to diagnose a Cu deficiency in Pinus radiata plants.

Vestibular-oculomotor interaction in cat eye-head movements

When cats make slow scanning head movements, intersaccadic counterrotary eye movements are driven by the vestibulo-ocular reflex, but reset or forward saccades are not directly affected by vestibular afference. When the movements are rapid (∼200 deg./sec), large (40°), and executed in single step shifts of gaze (whether in the dark or during visual fixation shifts between known targets), there is no longer any clear vestibular effect on any eye movements during the gaze shift. The vestibulo-ocular reflex is active only at the beginning of head rotation and again at its termination as the gaze reaches its goal, even in the absence of vision. It is postulated that head-in-space and eye-in-orbit movements are perfectly monitored to adjust the amplitude of gaze shifts, despite the lack of overt vestibular effects on eye movements.

Depth of Strabismic Amblyopia Determined with Neutral Density Filters

We used a neutral density filter to assess motor responses in the fixation patterns of 25 patients, ranging in age from 5 to 54 years, with strabismic amblyopia. Shifts of fixation back to the preferred eye occurred when the visual acuity of the preferred eye through the filter was marginally better than that of the amblyopic eye. Thus, we were able to correlate the level of the filter at which this shift occurred with the level of amblyopia. This technique may be particularly helpful in the examination of preliterate children and in monitoring the progress in the treatment of amblyopia.

POSSIBLE ALTERATIONS IN CORRESPONDENCE ASSOCIATED WITH ASYMMETRIC CONVERGENCE

Available nonius horopter data in asymmetric convergence has been reanalyzed by computing the binocular disparity of each horopter datum point relative to the Vieth - Müller circle. The results of this analysis on the best available data indicate that some corresponding points do shift upon asymmetric gaze. Because such convergence postures involve different eye movement innervational patterns, it is suggested that this is the cause of these apparent alterations. Some of the remaining data showed nonsystematic changes in experimental errors, suggesting that unintentional shifts in fixation may have occurred; unintentional tactile cues (used in making the actual settings) may have been present; and sampling errors may have influenced these particular findings.

Eye movements of monkeys during discrimination learning: Role of visual scanning.

Four experiments were conducted on stumptailed monkeys (Macaca arctoides) to determine whether the high levels of visual scanning (shifts in fixation from one discriminative stimulus to the other) seen during discrimination learning play a necessary role in this learning. In Experiments 1 and 2, the monkeys were given a series of two-choice, dot-pattern discrimination reversal problems. Normal visual scanning before a choice response was allowed during all but the reversal trials of half of the problems. On these latter trials, the discriminative stimuli were replaced by an uninformative stimulus after the animals made more than one visual fixation on each discriminative stimulus. Thus, on these trials, the animals were limited, in terms of the information received, to the empirically determined minimum number of scans necessary to maintain high levels of performance on such problems. In both experiments, which differed primarily in the number and type of uninformative stimuli used, the rate of reversal learning was markedly retarded by the experimental condition, with the effect persisting over a long series of problems. The magnitude of the effect was unrelated to the similarity of the uninformative stimulus to the discriminative stimuli. In Experiment 3, the monkeys were given a series of discrimination problems without reversals, during half of which the experimental condition was in effect. The results were similar to those of the first two experiments. Experiment 4 was similar to the preceding experiment except that, under the experimental condition, each trial began with the uninformative stimuli, which were replaced by the discriminative stimuli when visual scanning occurred. The uninformative stimuli had no clear-cut effect on discrimination learning in this experiment. These experiments indicate that the information provided by above-minimum levels of scanning is not necessary for discrimination learning per se, but it dose appear necessary for efficient discrimination learning.

Evoked potential correlates of visual selective attention

Two experiments are reported in which the relationship is explored between the N1 and P2 components of the visual evoked potential and visual selective attention. In both experiments, channels were defined in terms of stimulus attributes (experiment 1 — intensity; experiment 2 — shape) with all stimuli being presented at a common spatial locus in order to preclude fixation shifts. Under these circumstances, P2 was found in both experiments to correlate with visual selective attention whereas N1 did not. It is concluded from the null result for N1 that a precortical gating mechanism for visual inputs within a single spatial channel is not a component of the visual system. The P2 correlate of visual selective attention, because of its long latency, is attributed to the differential post-perceptual processing inevitably received by task-relevant and task-irrelevant inputs.

Experimental systolic and diastolic overloading in rats: total proteins turnover rate. Enzymatic and structural properties of myosin.

The fractional turnover rate of the total cardiac proteins has been measured by using the continuous infusion technique with 3H lysine. It augments by a factor of 3 in systolic as well as in diastolic overloading, but in the former the peak was reached within the first week after operation and in the later the peak was not reached until the 14th day. The myosin structure and enzymatic properties have been studied in several huge hypertrophic hearts (around 100% hypertrophy). In this condition the burst size of myosin is normal, as well as its K+ ATPase, but there is a sharp decline in the Ca2+ ATPase activity. Moreover, antibodies against native or defolded heavy meromyosin exhibit, a vertical shift in microcomplement fixation when made to react with molecules extracted from hypertrophied hearts. The normal isozymic pattern of rat heart myosin, as shown in non dissociating electrophoresis, was reversed.

Eye movements of stumptailed monkeys during discrimination learning: VTE revisited

Eye movements of stumptailed monkeys were measured during learning of a pattern discrimination problem. Amount of scanning (shifts in visual fixation from one pattern to the other) increased once learning began and reached a maximum either at about the point that frequency of correct responses reached asymptote or just after that. These results, taken together with earlier findings on vicarious trial and error and operant observing behavior, suggest that this is the characteristic pattern of change in frequency of observing during visual discrimination learning. A change in information processing strategy is proposed as one explanation for these results. Duration of the last fixation on a discriminative stimulus during a trial showed similar, though not identical, changes with practice. The decrease in duration of the last fixation following learning contrasts with results of prior studies involving more complex tasks, and supports our conclusion that the duration of the last fixation is particularly sensitive to the cognitive processing requirements of the discriminative task.

Eye Movements of Monkeys During Learning-Set Formation

Eye movements of stump-tailed monkeys were measured during learning of a long series of two-choice pattern discrimination problems. The amount of scanning per trial (shifts in visual fixation from one pattern to the other) and the duration of individual fixations on the patterns increased during the course of learning-set formation and (except for the amount of scanning by some animals) remained high during the prolonged training following learning-set formation. Some of the changes in eye movements were different from those seen during the learning of single discrimination problems, a difference that possibly reflects cognitive processes specific to the learning-set task.