NOTE ON SIMULTANEOUS DISCRIMINATION OF VISUAL ATTRIBUTES

van der H eijden A. H. C. Note on simultaneous discrimination of visual attributes. Scand. J. Psychol ., 1972, 13 , 71–72.—A tachistoscopically presented stimulus, provided it is above threshold, results in a visual image with a minimum duration of about 250 msec. In experiments on visual information processing, therefore, the results must be interpreted in terms of 'effective stimulus duration' (exposure time and duration of visual image) rather than exposure time alone.     

Attentional capacity is undifferentiated: concurrent discrimination of form, color, and motion

We report a series of experiments on the concurrent discrimination of form, color, and motion attributes. All tasks involved joint discrimination of attributes, and positions and were highly demanding of attention. We quantified interference between concurrent discriminations by establishing the attention-operating characteristic. Interference was indistinguishable for similar and dissimilar task combinations (form-form, color-color, motion-motion, and color-form, color-motion, motion-color, and motion-form, respectively). These results suggest strongly that different visual discriminations draw on the same attentional capacity--in other words, that the capacity of visual attention is undifferentiated.     

Visual discrimination of vowel duration

Discrimination of vowel duration was explored with regard to discrimination threshold, error bias, and effects of modality and consonant context. A total of 122 normal-hearing participants were presented with disyllabic-like items such as /lal-lal/ or /mam-mam/ in which the lengths of the vowels were systematically varied and were asked to judge whether the first or second vowel was longer. Presentation was either visual, auditory, or audiovisual. Vowel duration differences varied in 24 steps: 12 with a longer first /a/ and 12 with a longer last /a/ (range: ±33–400 ms). Results: 50% JNDs were smaller than the lowest tested step size (33 ms); 75% JNDs were in the 33–66 ms range for all conditions but V /lal/, with a 75% JND at 66–100 ms. Errors were greatest for visual presentation and for /lal-lal/ tokens. There was an error bias towards reporting the first vowel as longer, and this was strongest for /mam-mam/ and when both vowels were short, possibly reflecting a sublinguistic processing strategy.     

Impaired tactual perception in children with Down's syndrome

Using standardized neuropsychological tests, tactual finger discrimination, graphaesthesia and stereognosis were studied in a group of 11 children aged 7–11 years with Down's syndrome (DS). All tasks were solved without visual control. The performance was subnormal in each test and the results of the stereognosis test were particularly poor. It was ascertained that the DS children could understand test instructions. Moreover, under visual control all objects used in the stereognosis test were handled correctly. The results suggest that tactual perception is subnormal in children with DS. The pathogenesis of the somatosensory abnormalities should be explored.     

Lifespan changes in attention: The visual search task

There are two popular frameworks for the study of visual attention. Treisman's Feature Integration Theory focuses on the effortful process of binding together the multiple attributes of an object. Posner's Visual Orienting Theory emphasizes the movement of an attentional spotlight across space. Although both aspects are undoubtedly important in any visual search task, it is not clear how each of these aspects changes with age. We tested observers aged 6, 8, 10, 22, and 72 years on visual search tasks designed to isolate these factors. No age-related differences were found in single- or double-feature discrimination, attention movement to a single item, or search for a single-feature target among distractors. Two age-related changes were found: (1) young children were less able than either young adults or seniors to search for targets defined by a conjunction of features, and (2) both children and seniors were less able than young adults to move attention voluntarily from item to item. This implies that feature integration and voluntary movement of attention have different trajectories over the lifespan.     

High-fidelity perceptual long-term memory revisited--and confirmed

Experiments on short-term perceptual memory for elemental visual attributes, such as contrast, motion, orientation, and spatial frequency, have relied on a delayed discrimination technique in which the subject compares two stimuli presented at different points in time and memory is indexed by discrimination thresholds measured for the different time intervals between reference and test. In a variant of this procedure, used in experiments on long-term memory, the presentation of a single reference is followed by a memory test that combines two-alternative forced-choice decisions with the method of constant stimuli. With this procedure, it is impossible to distinguish the effects of criterion-setting processes and memory on performance, but this confound can be eliminated by testing many subjects and having each subject make a single decision. The resulting "group thresholds" are stable across time intervals of 24 hr, confirming previous findings of high-fidelity storage in the long-term memory range.     

Comparison at a distance

The visual system is known to contain hard-wired mechanisms that compare the values of a given stimulus attribute at adjacent positions in the visual field; but how are comparisons performed when the stimuli are not adjacent? We ask empirically how well a human observer can compare two stimuli that are separated in the visual field. For the stimulus attributes of spatial frequency, contrast, and orientation, we have measured discrimination thresholds as a function of the spatial separation of the discriminanda. The three attributes were studied in separate experiments, but in all cases the target stimuli were briefly presented Gabor patches. The Gabor patches lay on an imaginary circle, which was centred on the fixation point and had a radius of 5 deg of visual angle. Our psychophysical procedures were designed to ensure that the subject actively compared the two stimuli on each presentation, rather than referring just one stimulus to a stored template or criterion. For the cases of spatial frequency and contrast, there was no systematic effect of spatial separation up to 10 deg. We conclude that the subject's judgment does not depend on discontinuity detectors in the early visual system but on more central codes that represent the two stimuli individually. In the case of orientation discrimination, two naive subjects performed as in the cases of spatial frequency and contrast; but two highly trained subjects showed a systematic increase of threshold with spatial separation, suggesting that they were exploiting a distal mechanism designed to detect the parallelism or non-parallelism of contours.     

The effects of intradimensional and extradimensional shifts on visual discrimination learning in humans and non-human primates

Human subjects and non-human primates (the common marmoset) were trained on a series of reversals of both a simple (stimuli varying along one dimension) and compound (stimuli varying along two different dimensions) visual discrimination, using computer-generated stimuli. They were then shifted to a third series of reversals using completely novel compound stimuli. Those humans and marmosets for which the previously relevant dimension remained relevant, following the shift (shapes to shapes or lines to lines; intradimensional shift) made fewer errors than those for which the previously irrelevant dimension became relevant (shapes to lines or lines to shapes; extradimensional shift). These findings suggest that both humans and marmosets can learn to attend to the specific attributes or dimensions of a stimulus and use this information in visual discrimination learning.     

What happens to an individual visual working memory representation when it is interrupted?

This study tested the hypothesis that even the simplest cognitive tasks require the storage of information in working memory (WM), distorting any information that was previously stored in WM. Experiment 1 tested this hypothesis by requiring observers to perform a simple letter discrimination task while they were holding a single orientation in WM. We predicted that performing the task on the interposed letter stimulus would cause the orientation memory to become less precise and more categorical compared to when the letter was absent or when it was present but could be ignored. This prediction was confirmed. Experiment 2 tested the modality specificity of this effect by replacing the visual letter discrimination task with an auditory pitch discrimination task. Unlike the interposed visual stimulus, the interposed auditory stimulus produced little or no disruption of WM, consistent with the use of modality‐specific representations. Thus, performing a simple visual discrimination task, but not a simple auditory discrimination task, distorts information about a single feature being maintained in visual WM. We suggest that the interposed task eliminates information stored within the focus of attention, leaving behind a WM representation outside the focus of attention that is relatively imprecise and categorical.     

Assessment of visual acuity in preschool children

Abstract.— Problems in testing visual acuity of preschool children were discussed with regard to choice of optotype and test distance, illumination, instruction and response indicator, and the motivational aspect of the test situation. A test situation conforming to these requirements for measuring visual acuity was arranged for testing of preschool children, using a discrimination learning paradigm with simultaneous presentation of the cues. The test figures were two Landolt Cs of equal size but one with the gap filled in, thus forming a circle. Small toys were used as rewards for choosing the Landolt C. Of 27 children, 2–6 years of age, 25 achieved a visual acuity level corresponding to a Snellen value of 20/20. The results thus indicate a better visual acuity for preschool children than is commonly believed.     

On the benefits of transient attention across the visual field

There are well-known differences in resolution and performance across the visual field with performance generally better for the lower than the upper visual hemifield. Here we attempted to assess how transient attention summoned by a peripheral precue affects performance across the visual field. Four different attentional precueing tasks were used, varying in difficulty and attentional load. When a single discrimination target was presented (experiments 1 and 2), precues that summon transient attention had very little, if any, effect upon performance. However, when the target was presented among distractors (experiments 3 and 4), the precue had a substantial effect upon discrimination performance. The results showed that asymmetries in visual resolution between the upper and lower hemifields become more pronounced with increasing eccentricity. Furthermore, when the observers performed a precued acuity task with distractors, involving the judgment of the relative position of a small disk within a larger one, there was an asymmetry in the transient attentional effect on discrimination performance; the benefits of transient attention were larger in the upper than in the lower hemifield. Areas in the visual field where visual performance is generally worse thus appear to receive the largest attentional boost when needed. Possible ecological explanations for this are discussed.     

Processing of facial and non‐facial visual stimuli in 2–5‐year‐old children

The present experiments examined the degree to which analytic and holistic modes of processing play a role in the way 2–5‐year‐old children process facial and non‐facial visual stimuli. Children between 2 and 5 years of age were instructed to categorize faces (in Experiment 1) and non‐facial visual stimuli, such as birds and planes (in Experiment 2), into two categories. The categories were so constructed as to allow the children to categorize the facial and non‐facial stimuli either analytically (by focusing on a single attribute) or holistically (in terms of overall similarity). The results demonstrated that the previous conclusions concerning older children's (from 6 years onwards) holistic mode of facial processing could not be generalized to younger children because most of the 2–5‐year olds processed the faces by taking single facial attributes into account. A similar pattern of results emerged for the processing of objects, showing that the majority of the children focused on single attributes. Thus, for both visual domains, holistic processing was the exception rather than the rule. Copyright © 2002 John Wiley & Sons, Ltd.     

Measuring the effect of multiple eye fixations on memory for visual attributes

Because of limited peripheral vision, many visual tasks depend on multiple eye fixations. Good performance in such tasks demonstrates that some memory must survive from one fixation to the next. One factor that must influence performance is the degree to which multiple eye fixations interfere with the critical memories. In the present study, the amount of interference was measured by comparing visual discriminations based on multiple fixations to visual discriminations based on a single fixation. The procedure resembled partial report, but used a discrimination measure. In the prototype study, two lines were presented, followed by a single line and a cue. The cue pointed toward one of the positions of the first two lines. Observers were required to judge if the single line in the second display was longer or shorter than the cued line of the first display. These judgments were used to estimate a length threshold. The critical manipulation was to instruct observers either to maintain fixation between the lines of the first display or to fixate each line in sequence. The results showed an advantage for multiple fixations despite the intervening eye movements. In fact, thresholds for the multiple-fixation condition were nearly as good as those in a control condition where the lines were foveally viewed without eye movements. Thus, eye movements had little or no interfering effect in this task. Additional studies generalized the procedure and the stimuli. In conclusion, information about a variety of size and shape attributes was remembered with essentially no interference across eye fixations.     

大小数量加工机制分离现象的ERP研究

大量行为研究表明,个体对4以上非符号数量的加工存在加工机制分离现象,但是相关的神经机制研究还很少。本研究选取21名大学生被试,结合ERP技术和数量判断任务,以数量比率效应为指标,比较4以上不同大小数量加工的神经反应模式。结果显示,大小数量加工条件下数量比率效应对P2p成分幅值的调节模式存在显著差异。这支持了小数量加工基于数量属性,大数量加工基于非数量属性的观点。     

Measuring the effect of multiple eye fixations on memory for visual attributes.

Because of limited peripheral vision, many visual tasks depend on multiple eye fixations. Good performance in such tasks demonstrates that some memory must survive from one fixation to the next. One factor that must influence performance is the degree to which multiple eye fixations interfere with the critical memories. In the present study, the amount of interference was measured by comparing visual discriminations based on multiple fixations to visual discriminations based on a single fixation. The procedure resembled partial report, but used a discrimination measure. In the prototype study, two lines were presented, followed by a single line and a cue. The cue pointed toward one of the positions of the first two lines. Observers were required to judge if the single line in the second display was longer or shorter than the cued line of the first display. These judgments were used to estimate a length threshold. The critical manipulation was to instruct observers either to maintain fixation between the lines of the first display or to fixate each line in sequence. The results showed an advantage for multiple fixations despite the intervening eye movements. In fact, thresholds for the multiple-fixation condition were nearly as good as those in a control condition where the lines were foveally viewed without eye movements. Thus, eye movements had little or no interfering effect in this task. Additional studies generalized the procedure and the stimuli. In conclusion, information about a variety of size and shape attributes was remembered with essentially no interference across eye fixations.     

Visual long-term memory for spatial frequency?

It has been suggested that a visual long-term memory based on a sensory representation of the stimulus accounts for discrimination performance when the reference and the test stimuli are separated in time. Decision processes involved in setting response criteria, however, may also contribute to discrimination performance. In the present study, it is shown that under proper control, spatial frequency discrimination thresholds from a group of observers, each performing on a single trial, are significantly higher for a 2-h than for a 5-sec retention interval, whereas thresholds from individual observers performing in repeated trials with a 2-h retention interval are considerably lower. The results suggest that discrimination performance may depend on the retention of task-relevant information, such as a response criterion, rather than on visual memory of the stimulus. It is concluded that it is risky to postulate ahigh-fidelity long-term visual memory for spatial frequency on the basis of psychophysical group discrimination thresholds.     

Attention and multidimensional discrimination1

Observers’ ability to perform several discrimination tasks at the same time was tested using a two-alternative temporal forced-choice procedure. Discrimination of two auditory dimensions (pitch and intensity) and two visual dimensions (horizontal position and vertical position) was measured under conditions where one, two or all four dimensions required attention. Three signal durations were used: 67, 133, and 200 msec. Increasing the number of dimensions requiring attention systematically reduces the precisions of discrimination for each dimension. Auditory and visual discrimination is affected similarly. The amount of reduction in discrimination is independent of whether the dimensions requiring attention involve the same or different sensory modalities. The data are analyzed for evidence of a constant processing capacity employed in both single and multidimensional discrimination. The possibility that the observed performance levels could be achieved by sequentially processing the simultaneous inputs is also considered.     

Duration discrimination of empty and filled intervals marked by auditory and visual signals

Experiments 1 and 2 compared, with a single-stimulus procedure, the discrimination of filled and empty intervals in both auditory and visual modalities. In Experiment 1, in which intervals were about 250 msec, the discrimination was superior with empty intervals in both modalities. In Experiment 2, with intervals lasting about 50 msec, empty intervals showed superior performance with visual signals only. In Experiment 3, for the auditory modality at 250 msec, the discrimination was easier with empty intervals than with filled intervals with both the forced-choice (FC) and the single stimulus (SS) modes of presentation, and the discrimination was easier with the FC than with the SS method. Experiment 4, however, showed that at 50 and 250 msec, with a FC-adaptive procedure, there were no differences between filled and empty intervals in the auditory mode; the differences observed with the visual mode in Experiments 1 and 2 remained significant. Finally, Experiment 5 compared differential thresholds for four marker-type conditions, filled and empty intervals in the auditory and visual modes, for durations ranging from .125 to 4 sec. The results showed (1) that the differential threshold differences among marker types are important for short durations but decrease with longer durations, and (2) that a generalized Weber’s law generally holds for these conditions. The results as a whole are discussed in terms of timing mechanisms.     

Evidence against a central bottleneck during the attentional blink: multiple channels for configural and featural processing

When a visual target is identified, there is a period of several hundred milliseconds when the processing of subsequent targets is impaired, a phenomenon labeled the attentional blink (AB). The emerging consensus is that the identification of a visual target temporarily occupies a limited attentional resource that is essential for all visual perception. The present results challenge this view. With the same digit discrimination task that impaired subsequent letter discrimination for several hundred milliseconds, we found no disruption of subsequent face discrimination. These results suggest that all stimuli do not compete for access to a single resource for visual perception. We propose a multi-channel account of interference in the AB paradigm.     

Learning categories by touch: On the development of holistic and analytic processing

The development of holistic and analytic processing often studied in the visual domain was investigated in haptics. Children 3 to 9 years of age and adults had to categorize haptic exemplars that varied systematically in four attributes (size, shape, surface texture, and weight). The subjects could learn the categories either analytically--that is, by focusing on a single attribute--or holistically--that is, in terms of overall similarity. The data show that even the youngest children learned the haptic categories far more often in an analytic mode than in a holistic mode. Nevertheless, an age trend was observed, referring to the attributes that the analytic learners used for their categorization. The children preferred substance-related attributes, especially surface texture, whereas the adults preferred structure-related attributes, especially shape. Thus, it appears that analytic and/or holistic processing in category learning develops in a similar manner in the visual and haptic domains.