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Vision Research Feb 1999Fixation disparity, i.e. the vergence error within Panum's area, can be measured psychophysically with two nonius (vernier) lines that are presented dichoptically, i.e....
Fixation disparity, i.e. the vergence error within Panum's area, can be measured psychophysically with two nonius (vernier) lines that are presented dichoptically, i.e. one to each eye. The observer adjusts these nonius lines to subjective alignment; the resulting physical nonius offset indicates the amount of fixation disparity. The present experiments investigate the relation between fixation disparity and the nonius bias, which is the physical offset of the nonius lines that is adjusted by the observer in order to perceive them as aligned when both nonius lines are presented to both eyes (binocular nonius bias) or both to the left or both to the right eye (monocular nonius bias). It was found that (1) the fixation disparity is correlated with the binocular nonius bias in the horizontal and vertical meridian and (2) the binocular nonius bias can be predicted from the average of the right eye and left eye monocular nonius bias. To remove the influence of the nonius bias on measured fixation disparity it is possible to calculate the fixation disparity relative to the individual binocular nonius bias, rather than to the physical coincidence of the nonius lines. This procedure tends to increase the correlation between fixation disparity and the tonic resting position of vergence. We discuss the clinical relevance of the dichoptic nonius method for measuring fixation disparity and its limitations as compared to physical recordings of eye position.
Topics: Convergence, Ocular; Fixation, Ocular; Humans; Ocular Motility Disorders; Vision Disparity; Vision, Binocular
PubMed: 10341993
DOI: 10.1016/s0042-6989(98)00163-1 -
Vision Research Aug 2007Using a serial search paradigm, we observed several effects of within-object fixation position on spatial and temporal control of eye movements: the preferred viewing...
Using a serial search paradigm, we observed several effects of within-object fixation position on spatial and temporal control of eye movements: the preferred viewing location, launch site effect, the optimal viewing position, and the inverted optimal viewing position of fixation duration. While these effects were first identified by eye-movement studies in reading, our approach permits an analysis of the functional relationships between the effects in a different paradigm. Our results demonstrate that the fixation position is an important predictor of the subsequent saccade by influencing both fixation duration and the selection of the next saccade target.
Topics: Adult; Fixation, Ocular; Humans; Pattern Recognition, Visual; Photic Stimulation; Psychomotor Performance; Reading; Saccades; Time Factors
PubMed: 17662332
DOI: 10.1016/j.visres.2007.05.010 -
Vision Research Jun 2008A recent study by Poljac et al. [Poljac, E., Lankheet, M. J. M., & van den Berg, A. (2005). Perceptual compensation for eye torsion. Vision Research, 45(4), 485-496]...
A recent study by Poljac et al. [Poljac, E., Lankheet, M. J. M., & van den Berg, A. (2005). Perceptual compensation for eye torsion. Vision Research, 45(4), 485-496] concluded that there was complete perceptual compensation for ocular torsion, although they did not directly measure ocular torsion. Using a similar eccentric-gaze paradigm to induce changes in torsion, which were directly measured, we found inconsistent torsional eye movements at eccentric fixation, and also failed to detect a significant relationship between ocular torsion and the perception of line orientation. We then used a stimulus known to induce large changes in ocular torsion: on-centre yaw rotation. This stimulus induced a consistent change in the torsional position of the eye which positively correlated to subjects' visual perception of horizontal.
Topics: Adult; Eye Movements; Fixation, Ocular; Humans; Middle Aged; Orientation; Photic Stimulation; Reflex, Vestibulo-Ocular; Rotation; Visual Perception
PubMed: 18466947
DOI: 10.1016/j.visres.2008.03.012 -
Journal of Vision Jun 2016Two questions were posed in the present study: (1) Do infants search for discrepant items in the absence of instructions? We outline where previous research has been...
Two questions were posed in the present study: (1) Do infants search for discrepant items in the absence of instructions? We outline where previous research has been inconclusive in answering this question. (2) In what manner do infants search, and what are the fixation and saccade characteristics in saccadic search? A thorough characterization of saccadic search in infancy is of great importance as a reference for future eye-movement studies in infancy. We presented 10-month-old infants with 24 visual search displays in two separate sessions within two weeks. We report that infant saccadic search performance at 10 months is above what may be expected by our model of chance, and is dependent on the specific target. Infant fixation and saccade characteristics show similarities to adult fixation and saccade characteristics in saccadic search. All findings were highly consistent across two separate sessions on the group level. An examination of the reliability of saccadic search revealed that test-retest reliability for oculomotor characteristics was high, particularly for fixation duration. We suggest that future research into saccadic search in infancy adopt the presented model of chance as a baseline against which to compare search performance. Researchers investigating both the typical and atypical development of visual search may benefit from the presented results.
Topics: Female; Fixation, Ocular; Humans; Infant; Male; Pattern Recognition, Visual; Reproducibility of Results; Saccades
PubMed: 27299770
DOI: 10.1167/16.8.10 -
Scientific Reports Feb 2016As any cognitive task, visual search involves a number of underlying processes that cannot be directly observed and measured. In this way, the movement of the eyes...
As any cognitive task, visual search involves a number of underlying processes that cannot be directly observed and measured. In this way, the movement of the eyes certainly represents the most explicit and closest connection we can get to the inner mechanisms governing this cognitive activity. Here we show that the process of eye movement during visual search, consisting of sequences of fixations intercalated by saccades, exhibits distinctive persistent behaviors. Initially, by focusing on saccadic directions and intersaccadic angles, we disclose that the probability distributions of these measures show a clear preference of participants towards a reading-like mechanism (geometrical persistence), whose features and potential advantages for searching/foraging are discussed. We then perform a Multifractal Detrended Fluctuation Analysis (MF-DFA) over the time series of jump magnitudes in the eye trajectory and find that it exhibits a typical multifractal behavior arising from the sequential combination of saccades and fixations. By inspecting the time series composed of only fixational movements, our results reveal instead a monofractal behavior with a Hurst exponent , which indicates the presence of long-range power-law positive correlations (statistical persistence). We expect that our methodological approach can be adopted as a way to understand persistence and strategy-planning during visual search.
Topics: Fixation, Ocular; Humans; Photic Stimulation; Reading; Saccades; Visual Perception
PubMed: 26864680
DOI: 10.1038/srep20815 -
Journal of Vision Jan 2014Even though the dynamicity of our environment is a given, much of what we know on fixation selection comes from studies of static scene viewing. We performed a direct...
Even though the dynamicity of our environment is a given, much of what we know on fixation selection comes from studies of static scene viewing. We performed a direct comparison of fixation selection on static and dynamic visual stimuli and investigated how far identical mechanisms drive these. We recorded eye movements while participants viewed movie clips of natural scenery and static frames taken from the same movies. Both were presented in the same high spatial resolution (1080 × 1920 pixels). The static condition allowed us to check whether local movement features computed from movies are salient even when presented as single frames. We observed that during the first second of viewing, movement and static features are equally salient in both conditions. Furthermore, predictability of fixations based on movement features decreased faster when viewing static frames as compared with viewing movie clips. Yet even during the later portion of static-frame viewing, the predictive value of movement features was still high above chance. Moreover, we demonstrated that, whereas the sets of movement and static features were statistically dependent within these sets, respectively, no dependence was observed between the two sets. Based on these results, we argue that implied motion is predictive of fixation similarly to real movement and that the onset of motion in natural stimuli is more salient than ongoing movement is. The present results allow us to address to what extent and when static image viewing is similar to the perception of a dynamic environment.
Topics: Adult; Attention; Eye Movements; Female; Fixation, Ocular; Humans; Male; Motion Perception; Young Adult
PubMed: 24396045
DOI: 10.1167/14.1.2 -
Vision Research Jan 2013People can direct their gaze at a visual target for extended periods of time. Yet, even during fixation the eyes make small, involuntary movements (e.g. tremor, drift,... (Comparative Study)
Comparative Study
People can direct their gaze at a visual target for extended periods of time. Yet, even during fixation the eyes make small, involuntary movements (e.g. tremor, drift, and microsaccades). This can be a problem during experiments that require stable fixation. The shape of a fixation target can be easily manipulated in the context of many experimental paradigms. Thus, from a purely methodological point of view, it would be good to know if there was a particular shape of a fixation target that minimizes involuntary eye movements during fixation, because this shape could then be used in experiments that require stable fixation. Based on this methodological motivation, the current experiments tested if the shape of a fixation target can be used to reduce eye movements during fixation. In two separate experiments subjects directed their gaze at a fixation target for 17s on each trial. The shape of the fixation target varied from trial to trial and was drawn from a set of seven shapes, the use of which has been frequently reported in the literature. To determine stability of fixation we computed spatial dispersion and microsaccade rate. We found that only a target shape which looks like a combination of bulls eye and cross hair resulted in combined low dispersion and microsaccade rate. We recommend the combination of bulls eye and cross hair as fixation target shape for experiments that require stable fixation.
Topics: Eye Movements; Fixation, Ocular; Form Perception; Humans; Photic Stimulation
PubMed: 23099046
DOI: 10.1016/j.visres.2012.10.012 -
PloS One 2018Inaccuracy in the vergence eye position ("fixation disparity") can occur despite a fusion stimulus. When measured with eye trackers, this inaccuracy is referred to as...
Inaccuracy in the vergence eye position ("fixation disparity") can occur despite a fusion stimulus. When measured with eye trackers, this inaccuracy is referred to as "objective fixation disparity". It is a matter of debate whether objective fixation disparity can be estimated with a technically simple psycho-physical procedure, i.e. the perceived offset of aligned dichoptic nonius targets, referred to as "subjective fixation disparity". To investigate the relation between these two measures, simultaneous tests were made in far vision when placing prisms in front of the eyes (for a few seconds) in order to induce forced vergence, i.e. to vary the absolute disparity (from 1 deg divergent to 3.4 deg convergent). Frequent repeated measurements in 12 observers allowed for individual analyses. Generally, fixation disparity values and the effects of prisms were much smaller in the subjective than in the objective measures. Some observers differed systematically in the characteristics of the two types of prism-induced curves. Individual regressions showed that the subjective vs. objective slope was 8% on the average (with largest individual values of 18%). This suggests that sensory fusion shifts the visual direction of the (peripheral) binocular targets by the full amount of objective fixation disparity (since single vision was achieved); however, for the (central) monocular nonius lines this shift was more or less incomplete so that the dichoptic nonius targets indicated an individual percentage of objective fixation disparity. The subjective-to-objective ratio seems to be an individual characteristic of fixation disparity in terms of the amount and in terms of the effect of prism-induced forced vergence. Therefore, on the group level the subjective measures do not allow for a precise prediction of the objective measures.
Topics: Adult; Convergence, Ocular; Female; Fixation, Ocular; Humans; Male; Photic Stimulation; Vision Disparity; Young Adult
PubMed: 29980146
DOI: 10.1371/journal.pone.0199958 -
PloS One 2018Pupil diameter and microsaccades are captured by an eye tracker and compared for their suitability as indicators of cognitive load (as beset by task difficulty)....
Pupil diameter and microsaccades are captured by an eye tracker and compared for their suitability as indicators of cognitive load (as beset by task difficulty). Specifically, two metrics are tested in response to task difficulty: (1) the change in pupil diameter with respect to inter- or intra-trial baseline, and (2) the rate and magnitude of microsaccades. Participants performed easy and difficult mental arithmetic tasks while fixating a central target. Inter-trial change in pupil diameter and microsaccade magnitude appear to adequately discriminate task difficulty, and hence cognitive load, if the implied causality can be assumed. This paper's contribution corroborates previous work concerning microsaccade magnitude and extends this work by directly comparing microsaccade metrics to pupillometric measures. To our knowledge this is the first study to compare the reliability and sensitivity of task-evoked pupillary and microsaccadic measures of cognitive load.
Topics: Eye Movement Measurements; Female; Fixation, Ocular; Humans; Male; Pupil; Saccades; Visual Perception
PubMed: 30216385
DOI: 10.1371/journal.pone.0203629 -
PLoS Computational Biology Mar 2021Simple choices (e.g., eating an apple vs. an orange) are made by integrating noisy evidence that is sampled over time and influenced by visual attention; as a result,...
Simple choices (e.g., eating an apple vs. an orange) are made by integrating noisy evidence that is sampled over time and influenced by visual attention; as a result, fluctuations in visual attention can affect choices. But what determines what is fixated and when? To address this question, we model the decision process for simple choice as an information sampling problem, and approximate the optimal sampling policy. We find that it is optimal to sample from options whose value estimates are both high and uncertain. Furthermore, the optimal policy provides a reasonable account of fixations and choices in binary and trinary simple choice, as well as the differences between the two cases. Overall, the results show that the fixation process during simple choice is influenced dynamically by the value estimates computed during the decision process, in a manner consistent with optimal information sampling.
Topics: Choice Behavior; Fixation, Ocular; Humans; Models, Psychological; Psychometrics; Reaction Time
PubMed: 33770069
DOI: 10.1371/journal.pcbi.1008863