On Knowing Which Way to Trace: Direction Errors During Visual Curve Tracing.

McCormick and Jolicoeur's (1991; 1994) zoom lens model of visual curve tracing proposes that curve tracing involves tracking a curve with a variable size local operator. Unspecified in their model is how the executive function guiding the processing field of this operator initially knows which direction to trace. An experiment was conducted to determine whether observers occasionally curve trace in the wrong direction. A typical curve tracing task involving the determination of whether two dots occur on the same line in a display consisting of two dots and two intertwining lines was used. Lengthening the curve segment at the beginning of a to-be-traced curve resulted in a slowing of response times only to dot locations close to the end of the to-be-traced line. Apparently, observers calculate curve tracing direction based on the spatial location of the second (i.e., target) dot, which can result in erroneously tracing in the wrong direction at dot locations farther along the line. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Manipulating the shape of distance effects in visual curve tracing: Further evidence for the zoom lens model.

Reexamined the predictive power of the zoom lens curve tracing model in the research of P. A. McCormick and P. Jolicoeur (see record 1992-07800-001) by selectively manipulating distractor proximity in 4 conditions and regressing the predictions of the model on human response time. 12 university students participated. The model was compared with 2 other curve tracing models: pixel by pixel tracing and the bipartite receptive field operator of Jolicoeur et al (see record 1992-15217-001). Results provide strong support for McCormick and Jolicoeur's visual attention based zoom lens operator. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Postattentive vision.

Much research has examined preattentive vision: visual representation prior to the arrival of attention. Most vision research concerns attended visual stimuli; very little research has considered postattentive vision. What is the visual representation of a previously attended object once attention is deployed elsewhere? The authors argue that perceptual effects of attention vanish once attention is redeployed. Experiments 1–6 were visual search studies. In standard search, participants looked for a target item among distractor items. On each trial, a new search display was presented. These tasks were compared to repeated search tasks in which the search display was not changed. On successive trials, participants searched the same display for new targets. Results showed that if search was inefficient when participants searched a display the first time, it was inefficient when the same, unchanging display was searched the second, fifth, or 350th time. Experiments 7 and 8 made a similar point with a curve tracing paradigm. The results have implications for an understanding of scene perception, change detection, and the relationship of vision to memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mental curve tracing with elementary stimuli.

It has been proposed that certain spatial relations are determined by an operation, or "visual routine," that can trace along a boundary (Ullman, 1984), as supported by Jolicoeur, Ullman, & Mackay's (1986) finding that the time required to determine if 2 Xs are on the same curve increased monotonically with the separation of the Xs along that curve. In the present study the generality of the curve tracing hypothesis was explored across 4 experiments by using elementary stimuli that eliminated interweaving curves, displaced the fixation point away from the curves and target Xs, and provided a simple alternative to curve tracing—namely, determining whether or not the Xs fell on the same side of the figure. In Exps 1 and 2, Ss were instructed to decide if the 2 Xs fell on same or different curves. Mean reaction time (RT) for same trials increased monotonically with the distance separating the Xs. In Exps 3 and 4 alternatives to curve tracing were tested. For same trials the evidence strongly favored curve tracing. However, different trials were apparently solved on the basis of judgmental processes operating in parallel with curve tracing. Curve tracing rates fluctuated across experiments and seemed to be partially governed by the width of the "pathway" provided for the trace. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of attention on infants' preference for briefly exposed visual stimuli in the paired-comparison recognition-memory paradigm.

This study examined the effect of attention on 3- to 6-mo-olds' responses to briefly exposed visual stimuli. In Study 1, stimuli presented at 2.5 or 5.0 s resulted in a familiarity preference in a subsequent paired-comparison procedure. A novelty preference was found with 10.0- or 20.0-s exposure durations. In Study 2, a Sesame Street movie elicited heart-rate-defined attention phases and stimuli replaced Sesame Street during sustained attention, attention termination, or 5.0 s following attention termination. For 20 and 26-wk-olds, stimuli presented for 5.0 s during sustained attention resulted in a novelty preference similar to that found when exposure time was 20.0 s. The duration of stimulus exposure during sustained attention in the familiarization phase was positively correlated with the preference for the novel stimulus in the paired-comparison procedure. Thus, processing of briefly presented visual stimuli differs depending on the type of attention in which the infant is currently engaged. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanisms of directed attention in the human extrastriate cortex as revealed by functional MRI

A typical scene contains many different objects, but the capacity of the visual system to process multiple stimuli at a given time is limited. Thus, attentional mechanisms are required to select relevant objects from among the many objects competing for visual processing. Evidence from functional magnetic resonance imaging (MRI) in humans showed that when multiple stimuli are present simultaneously in the visual field, their cortical representations within the object recognition pathway interact in a competitive, suppressive fashion. Directing attention to one of the stimuli counteracts the suppressive influence of nearby stimuli. This mechanism may serve to filter out irrelevant information in cluttered visual scenes.     

Depth perception in a stereoscopic display as a function of number of stimuli, depth range, and number of scale markers.

Ss were tested on 2 tasks, ranking dots in order of depth and specifying actual depth in space, to determine the effects of number of stimuli, depth range, and number of scale markers on depth discrimination. When ranking was required, increasing the number of dots presented resulted in decreased accuracy. The number of dots did not affect accuracy when specific depth assignments were required. Increasing the number of dots resulted in significantly greater time to complete the task. As depth range was increased, accuracy improved regardless of task and time scores decreased for the ranking task. Decrease in number of scale markers resulted in increased time and error scores. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceived numerosity: An information processing analysis.

Presented 3 university students with matrices of from 1 to 16 dots and asked them to count the dots they could see. In Condition 1 a visual noise pattern followed the display of dots by one of several intervals in order to control the time available to process them. In Condition 2 no mask was used, but the exposure duration was varied. In the processing time condition, dots were counted at a rate of 4 msec/dot when less than 6 dots were presented, and at a rate of 60 msec/dot for all dots in excess of 6. If enough time was given to process all the dots presented, virtually all were reported, whereas, if enough time was given to count only some of the dots, virtually none of the excess were counted. In the duration condition, in which processing time was not restricted, counting appeared to be a function of the visibility of the dots, as shown by a family of more linear functions between number of dots presented and number counted, with the slope determined by the duration of exposure. Data are consistent with a serial processing interpretation of dot counting occurring at a very early stage of information extraction, in which there is a serial scanning mechanism which extracts information from an initial brief store and transfers it to a 2nd store for actual counting. (French summary) (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Masking by object substitution: Dissociation of masking and cuing effects.

In a newly discovered form of visual masking, a target stimulus is masked by 4 flanking dots if their offset is delayed relative to the target (V. Di Lollo, J. T. Enns, & R. A. Rensink, 2000). In Di Lollo et al. (2000), the dot pattern also cued the relevant target and therefore required deliberate attention. In the present Experiments 2-6, a central arrow cued 1 of 2 letters for an E/F discrimination, with dots flanking both letters. Masking was reduced compared with the mask-cue procedure but was still robust. Delayed-offset dots flanking the nontarget also impaired performance, indicating competition for attention. Masking was unaffected by brightness of the dots relative to the target. Masking was attenuated not only by precuing attention to the target location but also by preview of an uninformative dot mask. Theories of masking by object substitution must therefore accommodate the prior context into which the target stimulus is introduced. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sustained attention after severe closed head injury.

Sustained attention was assessed in 20 patients with severe closed head injury (CHI) and 20 normal matched controls. Participants were presented with a visual continuous performance task (CPT) with 3 levels of complexity. Performance was assessed by examining response latencies and error rates. Across all levels of complexity, the CHI patients demonstrated a vigilance decrement, whereas the performance of the matched controls was stable across time. The vigilance decrement was not differentially affected by the manipulation of task complexity in the CHI patients. However, findings suggest that the overall vigilance performance of CHI patients was differentially affected by increasing the complexity of the task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Distributed and focused attention: Neuropsychological evidence for separate attentional mechanisms when counting and estimating.

Evidence is presented for 2 modes of attention operating in simultanagnosia. The authors examined visual enumeration in a patient, GK, who has severe impairments in serially scanning across a scene and is unable to count the numbers of items in visual displays. However, GK's ability to judge the relative magnitude of 2 displays was consistently above chance, even when overall luminosity did not vary with the number of items present. In addition, several variables had a differential impact on GK's counting and magnitude estimation. Magnitude estimation but not counting was facilitated by using elements that grouped more easily and by presenting the elements in regular configurations. In contrast, counting was facilitated by placing the elements in different colors while magnitude estimation was disrupted. Also GK's performance on magnitude estimation tasks was disrupted by asking him to count the elements present. The data suggest that GK can process visual stimuli in either a focused or distributed attention mode. When in a focused attention mode, performance is limited by poor serial scanning of attention due to an impaired explicit representation of visual space. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attention to combined attention in New World monkeys (Cebus apella, Saimiri sciureus).

Co-orientation by capuchin (Cebus apella) and squirrel (Saimiri sciureus) monkeys in response to familiar humans abruptly switching the direction of their visual attention was recorded. Co-orientation occurred more frequently overall in capuchins than squirrel monkeys. Capuchins showed a tendency to habituate within trials involving consecutive attention switches performed by 2 different people, whereas squirrel monkeys co-oriented more when the 2nd attention switch was by a 2nd actor. These results suggest variable attention-processing abilities in New World monkeys, including differences in summation of attention by others. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of interresponse time reinforcement on signalled-reward effect.

Examined the conditions under which presenting a signal for reinforcement decreases or increases the rate of leverpressing in rats. Response rate on a variable-interval (VI) schedule of reinforcement was decreased by a brief signal for reinforcement. In Experiment 1, requiring 1 short IRT to occur on completion of the VI requirement attenuated this response decrement. Requiring three responses to be emitted within a minimum amount of time at the end of the VI resulted in the reinforcement signal's enhancement of response rates. Experiment 2 replicated this increase in responding and showed that the reinforcement signal attenuated response rates on a simple VI schedule that yielded the same overall rate of reinforcement. In Experiment 3, the reinforcement signal enhanced response rates when 3 responses were required at the end of a VI schedule, but the signal attenuated response rates when the 3 responses could occur at any time in relation to the VI. These results suggest that the pattern of responding emitted immediately prior to reinforcement is a critical factor in determining the effect of reinforcement signal on response rate. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ultrastructure of the eggs of Culicoides circumscriptus, Culicoides gejgelensis, and Culicoides imicola (Diptera:Ceratopogonidae)

PURPOSE: To describe a newly identified clinical entity tentatively named white dot fovea. METHODS: We examined by scanning laser ophthalmoscopy 58 eyes of 30 patients (mean age, 64 years) who had white dots in the fovea (anatomically defined as the foveola) simulating macular hole. In addition, the retinal surfaces of 30 autopsy eyes from donors aged 70 years or older were observed by scanning electron microscopy. RESULTS: White dot fovea was bilateral in 28 of 30 patients (93%). It was characterized by the presence of numerous white dots on the foveal surface distributed either diffusely or along the foveal margin, forming a gray ring. There was no subjective symptom or visual disturbance. The condition was best seen by a scanning laser ophthalmoscope using argon blue laser as the light source. The white dots numbered from 100 to 300 per eye. Each dot was approximately 5 microns in diameter. Scanning electron microscopy showed foveal granules simulating the white dots in five of 30 autopsy eyes (17%). The granules had multiple protrusions with cilia-like structures resembling glial cells. This glia-like structure seemed to be a counterpart of clinically observed white dot fovea. CONCLUSION: White dot fovea is a new, frequent, and apparently innocuous clinical entity. It merits due attention in the differential diagnosis of macular holes.     

The origins of joint visual attention in infants.

Two experiments examined the origins of joint visual attention with a training procedure. In Experiment 1, infants aged 6-11 months were tested for a gaze-following (joint visual attention) response under feedback and no feedback conditions. In Experiment 2, infants 8-9 months received feedback for either following the experimenter's gaze (natural group) or looking to the opposite side (unnatural group). Results of the 2 experiments indicate that (a) joint visual attention does not reliably appear prior to 10 months of age, (b) from about 8 months of age, a gaze-following response can be learned, and (c) simple learning is not sufficient as the mechanism through which joint attention cues acquire their signal value. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Attention gating in short-term visual memory.

Investigated attention shift to a stream of numerals, in rapid serial visual presentation, using 3 graduate students with normal or corrected-to-normal vision. Ss detected a target embedded in a stream of letters presented at the left of fixation and, as quickly as possible, shifted their attention to a stream of numerals at the right of fixation. They attempted to report, in order, the 4 earliest occurring numerals after the target. Numerals appeared at rates of 4.6, 6.9, 9.2, and 13.4 sec. Analyses demonstrated that, for all Ss, targets, and numeral rates, the relative position of numerals in the response sequence showed clustering, disorder, and folding. Reported numerals tended to cluster around a stimulus position 400 msec after the target. Numerals were reported in an apparently haphazard order. The actual order of report resulted from a mixture of correctly ordered numerals with numerals ordered in the direction opposite to their order of presentation. Results are quantitatively described by a strength theory of order and are efficiently predicted by a computational attention gating model (AGM). The AGM may be derived from a more general attention model that assumes that (a) after detection of the target, an attention gate opens briefly to allow numerals to enter a visual short-term memory and (b) subsequent order of report depends on both item strength (how wide the gate was open during the numeral's entry) and on order information (item strength times cumulative strength of prior numerals). (78 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Peripheral stimulus localization by infants: Attention, age, and individual differences in heart rate variability.

The effect of attention to a focal stimulus on 3- to 6-month-old infants' peripheral stimulus localization was examined. Fixation was engaged on a central visual stimulus, and a stimulus was presented in the periphery after discrete time intervals (0 to 12 s) or until changes in heart rate (HR) occurred. Peripheral stimulus localization occurred less frequently when a significant HR deceleration had occurred (sustained attention) than when HR had returned to its prestimulus level (attention termination). A signal detection analysis showed that response bias was altered by attention and that during inattention infants with high HR variability were more likely to shift fixation away from the central stimulus independently of the presence of the peripheral stimulus. These data suggest that infant attention affects decision processes for continuing focal stimulus fixation rather than peripheral stimulus discriminability. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Impact of mental operation instructions.

Experiments were conducted to test the impact of embedding mental action verbs within instructions. Experiment 1 examined the instructional effects of these verbs on response time to a visual stimulus. Significant response time differences resulted from instructing participants to engage in different mental actions. Using Multidimensional Scaling, Experiment 2 explored how people understand the relationships amongst mental action verbs, resulting in a single "level of processing" dimension. Experiment 3 was designed to further explore the relationship of these verbs to cognition and behaviour. Signal detection analysis was used to determine if participants were shifting their criterion depending on the level of processing suggested in the instruction. Results showed an effect of instruction on response time, but not on criterion, sensitivity, or accuracy. Response time effects were found that were consistent with differences in word characteristics, including meaning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Supramodal and modality-specific mechanisms for stimulus-driven shifts of auditory and visual attention.

Describes 2 experiments in which visual and/or auditory location precues preceded visual or auditory targets. 30 observers were required to judge the location of the targets. Conditions were such that involuntary, stimulus-driven (SD) attention shifts were the only ones likely to occur and give rise to cueing effects. It was found that visual precues affected response time to localize both visual targets and auditory targets, but auditory precues affected only the time to localize auditory targets. Moreover, when visual and auditory cues conflicted, visual cues dominated in the visual task but were dominated by auditory cues in the auditory task. Results suggest that involuntary SD attention shifts might be controlled by a modality-specific mechanism for visual tasks, whereas SD shifts of auditory attention are controlled by a supramodal mechanism. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The impact of salient advertisements on reading and attention on web pages.

Human vision is sensitive to salient features such as motion. Therefore, animation and onset of advertisements on Websites may attract visual attention and disrupt reading. We conducted three eye tracking experiments with authentic Web pages to assess whether (a) ads are efficiently ignored, (b) ads attract overt visual attention and disrupt reading, or (c) ads are covertly attended with distraction showing up indirectly in the reading performance. The Web pages contained an ad above a central text and another ad to the right of the text. In Experiments 1, 2, and 3A the task was to read for comprehension. Experiment 1 examined whether the degree of animation affects attention toward the ads. The results showed that ads were overtly attended during reading and that the dwell times on ads were the longest when the ad above was static and the other ad was animated. In Experiments 2 and 3, the ads appeared abruptly after a random time interval. The results showed that attention (i.e., the time when the eyes first entered an ad) was related to the ad onset time. This happened especially for the ad to the right, indicating that ads appearing close to the text region capture overt attention. In Experiment 3B the participants browsed the Web pages according to their own interest. The study demonstrated that salient ads attract overt visual attention and disrupt reading, but during free browsing, ads were viewed more frequently and for longer time than during reading. (PsycINFO Database Record (c) 2011 APA, all rights reserved)