1,721,001 research outputs found
Is object search mediated by object-based or image-based representations?
No full textRecent research suggests that visually specific memory representations for previously fixated objects are maintained during scene perception. Here we investigate the degree of visual specificity by asking whether the memory representations are image-based or object-based. To that end we measured the effects of object orientation on the time to search for a familiar object from amongst a set of 7 familiar distractors arranged in a circular array. Search times were found to depend on the relative orientations of the target object and the probe object for both familiar and novel objects. This effect was found to be partly an image matching effect but there was also an advantage shown for the object's canonical view for familiar objects. Orientation effects were maintained even when the target object was specified as having unique or similar shape properties relative to the distractors. Participants' eye movements were monitored during two of the experiments. Eye movement patterns revealed selection for object shape and object orientation during the search process. Our findings provide evidence for object representations during search that are detailed and share image-based characteristics with more high-level characteristics from object memory
Face detection in peripheral vision: do faces pop out?
No full textWe examined whether faces can produce a 'pop-out' effect in visual search tasks. In the first experiment, subjects' eye movements and search latencies were measured while they viewed a display containing a target face amidst distractors. Targets were upright or inverted faces presented with seven others of the opposite polarity as an 'around-the-clock' display. Face images were either photographic or 'feature only', with the outline removed. Naive subjects were poor at locating an upright face from an array of inverted faces, but performance improved with practice. In the second experiment, we investigated systematically how training improved performance. Prior to testing, subjects were practised on locating either upright or inverted faces. All subjects benefited from training. Subjects practised on upright faces were faster and more accurate at locating upright target faces than inverted. Subjects practised on inverted faces showed no difference between upright and inverted targets. In the third experiment, faces with 'jumbled' features were used as distractors, and this resulted in the same pattern of findings. We conclude that there is no direct rapid 'pop-out' effect for faces. However, the findings demonstrate that, in peripheral vision, upright faces show a processing advantage over inverted faces
Eye scanning of multi-element displays. II. Saccade planning
No full textThe properties of saccadic eye movements were studied in a task that required observers to scan through a display consisting of a set of discrete objects. The saccades forming the scanpath showed very high accuracy with almost no undershoot provided no distractor item was located within a critical region around the saccade target. When a distractor item was located in the critical region, saccade accuracy was impaired. This result suggests that the intrinsic spatial selection process for saccadic scanning movements is of low resolution. The initial saccade following display onset showed different properties. The instructions required the observer to look first at a clearly distinct target at the top left of the display. However, the first saccade frequently showed ‘oculomotor capture’ and was directed either to a different item in the display, or to a midway location between items. The fixation following such erroneous first saccades was generally very short and showed a substantial drift towards the instructed location
Limb activation and the rehabilitation of unilateral neglect: evidence of task specific effects
No full textThe present study investigated the effectiveness of limb activation as a rehabilitation technique for visual neglect. Patients made left limb movements in left space or right limb movements in left space and performance was compared to that under no-limb-movement control conditions. The effects observed on a simple digit report task were equivocal and limb activation did not produce consistent improvements in the patients' ability to report left-sided stimuli. In a second study, the patients' eye movements were recorded while they performed a simple overt orienting task under limb activation conditions. There was no improvement in the leftward saccades made by any patient under either limb activation condition. A third study examined the effects of limb activation on the frequency of whole-word omissions in text reading. The number of left-sided whole-word omissions was reliably reduced with concurrent left limb activation. Furthermore, a smaller reduction in whole-word omissions was observed following right limb activation. It was also found that left-sided word omissions were reduced when limb activation was performed prior to the reading task, rather than concurrently. It is suggested that limb activation may improve overt orienting in tasks requiring voluntary control, but not when the task has an automatic reflexive component
The rhythm of the eyes: overt and covert attentional pointing
No full textThis commentary centres around the system of human visual attention. Although generally supportive of the position advocated in the target article, we suggest that the detailed account overestimates the capacities of active human vision. Limitations of peripheral search and saccadic accuracy are discussed in relation to the division of labour between covert and overt attentional processes
Saccades without eye movements
No full textWhen reading text, human subjects use a pattern of eye movements consisting of fast saccadic movements and fixations1. We have found a subject who cannot make eye movements. Her visual perception is surprisingly normal and she is able to read at high speeds. She uses movements of the head to compensate for the absence of eye movements. Her head movements during reading have a saccadic character and show many of the features that characterize eye movement
Using the eye-movement system to control the head
No full textWe tested the hypothesis that A.I., a subject who has total opthalmoplegia, resulting in a lack of eye movements, used her head to orientate in a qualitatively similar way to eye-based orientating of control subjects. We used four classic eye-movement paradigms and measured A.I.'s head movements while she performed the tasks. These paradigms were (i) the gap paradigm, (ii) the remote-distractor effect, (iii) the anti-saccade paradigm, and (iv) tests of saccadic suppression. In all cases, A.I.'s head saccades were qualitatively similar to previously reported eye-movement data. We conclude that A.I.'s head movements are probably controlled by the same neural mechanisms that control eye movements in unimpaired subjects
Rapid detection of person information in a naturalistic scene
Full text linkpreferential-looking paradigm was used to investigate how gaze is distributed in naturalistic scenes. Two scenes were presented side by side: one contained a single person (person-present) and one did not (person-absent). Eye movements were recorded, the principal measures being the time spent looking at each region of the scenes, and the latency and location of the first fixation within each trial. We studied gaze patterns during free viewing, and also in a task requiring gender discrimination of the human figure depicted. Results indicated a strong bias towards looking to the person-present scene. This bias was present on the first fixation after image presentation, confirming previous findings of ultra-rapid processing of complex information. Faces attracted disproportionately many fixations, the preference emerging in the first fixation and becoming stronger in the following ones. These biases were exaggerated in the gender-discrimination task. A tendency to look at the object being fixated by the person in the scene was shown to be strongest at a slightly later point in the gaze sequence. We conclude that human bodies and faces are subject to special perceptual processing when presented as part of a naturalistic scene
The effective fusional range for words in a natural viewing situation
No full textAbstractWe investigated the effective fusional range for written stimuli in children and adults in a natural viewing situation. We recorded binocular eye movements in children and adults during processing of stereoscopically presented words in a lexical decision task. The effect of disparity magnitude on ease of fusion caused decreased response accuracy, increasing numbers of fixations and increased trial viewing times when retinal disparity exceeded one character space. The data suggest that retinal inputs of a word that are disparate by up to one character (0.37°) fall within the effective fusional range such that lexical decisions are not impaired
Saccade target selection in visual search: the effect of information from the previous fixation.
No full textThis paper reports an analysis of saccades made during a task of visual search for a colour shape conjunction. The analysis concentrates on the saccade following the first saccade, thus complementing an earlier paper where the first saccades were analysed. The further analysis addresses the issue of what information might be held in trans-saccadic memory. As with the first saccade, incorrect second saccades tend to fall on distractors sharing one feature with the target. The proximity of the target to the fixation location immediately prior to the saccade is a very significant determinant of whether the saccade will reach the target. The results lead to the conclusion that in the majority of cases, choice of saccade destination is made afresh during each fixation with no carry-over from the previous fixation. However, in a small number of cases, second saccades are made after extremely brief fixation intervals. Although these saccades show a similar probability of reaching the target as those following longer fixations, it is argued that this sub-set of saccades are pre-programmed at the time of the preceding saccade
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