Orientation discrimination across the visual field: size estimates near contrast threshold

Performance in detection and discrimination tasks can often be made equal across the visual field through appropriate stimulus scaling. The parameter E2 is used to characterize the rate at which stimulus dimensions (e.g., size or contrast) must increase in order to achieve foveal levels of performance. We calculated both size and contrast E2 values for orientation discrimination using a spatial scaling procedure that involves measuring combination size and contrast thresholds for stimuli with constant size-to-contrast ratios. E2 values for size scaling were 5.77 degrees and 5.92 degrees. These values are three to four times larger than those recovered previously using similar stimuli at contrasts well above detection threshold (Sally & Gurnsey, 2003). E2 values for contrast scaling were 324.2 degrees and 44.3 degrees, indicating that for large stimuli little contrast scaling (.3% to 2.3% increase) was required in order to equate performance in the fovea and the largest eccentricity (10 degrees). A similar pattern of results was found using a spatial scaling method that involves measuring contrast thresholds for target identification as a function of size across eccentricities. We conclude that the size scaling for orientation discrimination at near-threshold stimulus contrasts is much larger than that required at suprathreshold contrasts. This may arise, at least in part, from contrast-dependent changes in mechanisms that subserve task performance.     

PROMOTING STIMULUS CONTROL WITH TEXTUAL PROMPTS AND PERFORMANCE FEEDBACK FOR PERSONS WITH MILD DISABILITIES

We assessed whether written task analyses would serve as textual prompts for performing functional tasks by persons with mild disabilities. Several variables that could influence the effectiveness of textual prompts to promote stimulus control were examined across four groups. A consistent finding was that written specific task analyses combined with end-of-trial performance feedback were effective for promoting the acquisition and generalization of several tasks. Performance transferred immediately to natural discriminative stimuli when the written task analyses and feedback were withdrawn for most tasks and participants. For 2 participants, transfer of stimulus control was accomplished by prompt fading, using individualized written task analyses either with or without performance feedback (Group 1). When feedback was not provided, the effectiveness of written specific task analyses was inconsistent across groups. In contrast to the controlling effects of written specific task analyses, written generic task analyses, which specified only major task outcomes, when combined with performance feedback (Group 1) did not control responding. Overall, this research demonstrated the effectiveness of written specific task analyses and performance feedback to promote stimulus control for persons with mild disabilities.     

Contrast thresholds for identification of numeric characters in direct and eccentric view

Aubert and Foerster (1857) are frequently cited for having shown that the lower visual acuity of peripheral vision can be compensated for by increasing stimulus size. This result is seemingly consistent with the concept of cortical magnification, and it has been confirmed by many subsequent authors. Yet it is rarely noted that Aubert and Foerster also observed a loss of the "quality of form." We have studied the recognition of numeric characters in foveal and eccentric vision by determining the contrast required for 67% correct identification. At each eccentricity, the lowest contrast threshold is achieved with a specific stimulus size. But the contrast thresholds for these optimal stimuli are not independent of retinal eccentricity as cortical magnification scaling would predict. With high-contrast targets, however, threshold target sizes were consistent with cortical magnification out to 6 degrees eccentricity. Beyond 6 degrees, threshold target sizes were larger than cortical magnification predicted. We also investigated recognition performance in the presence of neighboring characters (crowding phenomenon). Target character size, distance of flanking characters, and precision of focusing of attention all affect recognition. The influence of these parameters is different in the fovea and in the periphery. Our findings confirm Aubert and Foester's original observation of a qualitative difference between foveal and peripheral vision.     

Test–retest reliability and task order effects of emotional cognitive tests in healthy subjects

Little is known of the retest reliability of emotional cognitive tasks or the impact of using different tasks employing similar emotional stimuli within a battery. We investigated this in healthy subjects. We found improved overall performance in an emotional attentional blink task (EABT) with repeat testing at one hour and one week compared to baseline, but the impact of an emotional stimulus on performance was unchanged. Similarly, performance on a facial expression recognition task (FERT) was better one week after a baseline test, though the relative effect of specific emotions was unaltered. There was no effect of repeat testing on an emotional word categorising, recall and recognition task. We found no difference in performance in the FERT and EABT irrespective of task order. We concluded that it is possible to use emotional cognitive tasks in longitudinal studies and combine tasks using emotional facial stimuli in a single battery.     

Gaze behavior in face comparison: The roles of sex, task, and symmetry

Knowing where people look on a face provides an objective insight into the information entering the visual system and into cognitive processes involved in face perception. In the present study, we recorded eye movements of human participants while they compared two faces presented simultaneously. Observers’ viewing behavior and performance was examined in two tasks of parametrically varying difficulty, using two types of face stimuli (sex morphs and identity morphs). The frequency, duration, and temporal sequence of fixations on previously defined areas of interest in the faces were analyzed. As was expected, viewing behavior and performance varied with difficulty. Interestingly, observers compared predominantly the inner halves of the face stimuli—a result inconsistent with the general left-hemiface bias reported for single faces. Furthermore, fixation patterns and performance differed between tasks, independently of stimulus type. Moreover, we found differences in male and female participants’ viewing behaviors, but only when the sex of the face stimuli was task relevant.     

Parafoveal attention in congenitally deaf and hearing young adults

This reaction-time study compared the performance of 20 congenitally and profoundly deaf, and 20 hearing college students on a parafoveal stimulus detection task in which centrally presented prior cues varied in their informativeness about stimulus location. In one condition, subjects detected a parafoveally presented circle with no other information being present in the visual field. In another condition, spatially complex and task-irrelevant foveal information was present which the subjects were instructed to ignore. The results showed that although both deaf and hearing people utilized cues to direct attention to specific locations and had difficulty in ignoring foveal information, deaf people were more proficient in redirecting attention from one spatial location to another in the presence of irrelevant foveal information. These results suggest that differences exist in the development of attentional mechanisms in deaf and hearing people. Both groups showed an overall right visual-field advantage in stimulus detection which was attenuated when the irrelevant foveal information was present. These results suggest a left-hemisphere superiority for detection of parafoveally presented stimuli independent of cue informativeness for both groups.     

Bingo! Externally supported performance intervention for deficient visual search in normal aging, Parkinson's disease, and Alzheimer's disease

External support may improve task performance regardless of an individual's ability to compensate for cognitive deficits through internally generated mechanisms. We investigated if performance of a complex, familiar visual search task (the game of bingo) could be enhanced in groups with suboptimal vision by providing external support through manipulation of task stimuli. Participants were 19 younger adults, 14 individuals with probable Alzheimer's disease (AD), 13 AD-matched healthy adults, 17 non-demented individuals with Parkinson's disease (PD), and 20 PD-matched healthy adults. We varied stimulus contrast, size, and visual complexity during game play. The externally supported performance interventions of increased stimulus size and decreased complexity resulted in improvements in performance by all groups. AD also obtained benefit from increasing contrast, presumably by compensating for their contrast sensitivity deficit. The general finding of improved performance across healthy and afflicted groups suggests the value of visual support as an easy-to-apply intervention to enhance cognitive performance.     

Influence of short-term memory codes on visual image processing: evidence from image transformation tasks.

Three experiments showed that phonological recording of visual stimuli in short-term memory (STM) affects coding in long-term memory (LTM) and therefore performance on tasks involving generation and manipulation of visual images of the stimuli. An image transformation task was devised. It consists of mentally subtracting a part of an image to discover in the remainder another object. In Experiment 1, Ss were required to learn a set of easily nameable visual stimuli and then perform the subtraction task on images retrieved from LTM. Performance was significantly better when initial learning was accompanied by articulatory suppression (AS). Experiment 2 confirmed that AS had no effect when the task was performed on an image of a just-presented stimulus. In Experiment 3, the nameability of the stimuli was manipulated. The results replicated the effect of AS for items that were easy to name but showed no effect of AS for stimuli that were difficult to name.     

Reconfiguration of task-set: Is it easier to switch to the weaker task?

Switching between two tasks afforded by the same stimuli results in slower reactions and more errors on the first stimulus after the task changes. This “switch cost” is reduced, but not usually eliminated, by the opportunity to prepare for a task switch. While there is agreement that this preparation effect indexes a control process performed before the stimulus, the “residual” cost has been attributed to several sources: to a control process essential for task-set reconfiguration that can be carried out only after the stimulus onset, to probabilistic failure to engage in preparation prior to the stimulus, and to two kinds of priming from previous trials: positive priming of the now-irrelevant task set and inhibition of the now-relevant task-set. The main evidence for the carry-over of inhibition is the observation that it is easier to switch from the stronger to the weaker of a pair of tasks afforded by the stimulus than vice versa. We survey available data on interactions between task switching and three manipulations of relative task strength: pre-experimental experience, stimulus-response compatibility, and intra-experimental practice. We conclude that it is far from universally true that it is easier to switch to the weaker task. Either inhibition of the stronger task-set is a strategy used only in the special case of extreme inequality in strength, or its consequences for later performance may be masked by slower post-stimulus control operations for more complex tasks. Inhibitory priming may also be stimulus specific. Received: 31 March 1999 / Accepted: 23 July 1999     

Mental effort causes vigilance decrease due to resource depletion

The resource view on vigilance performance was tested. First, a low demanding task was compared with a similar low demanding task in which stimulus presentation was less monotonous due to added, irrelevant, stimuli. The resource view, maintaining that vigilance is lowered by hard mental work, predicts that addition of irrelevant stimuli will not affect performance. The classic arousal theory, however, states that arousal drops due to monotonous stimulus presentation and predicts that decreasing monotony will enhance performance. Results showed that performance was unaffected by added stimuli. Second, we tested whether a high-demanding task (with identical stimulus presentation as the low demanding task, but different instruction) would cause a greater decline in performance than the low demanding task. Indeed, in the high-demanding task performance was affected most. In sum, it appears that vigilance decreases due to hard mental work, which requires many resources. Both overall performance and decrement in performance can be explained in terms of resources, and this suggests that vigilance tasks should be resource-demanding tasks, which do not have to be of long duration.     

Keeping Simon simple: Examining the relationship between sequential modulations and feature repetitions with two stimuli, two locations and two responses

The present study examined performance across three two-choice tasks that used the same two stimuli, the same two stimulus locations, and the same two responses to determine how task demands can alter the Simon Effect, its distribution across reaction time, and its sequential modulation. In two of the tasks, repetitions of stimulus features were not confounded with sequences of congruent and incongruent trials. This attribute allowed us to investigate the sequential modulation of the Simon Effect in a two-choice task while equalizing the occurrence of feature repetitions. All tasks showed a similar sequential modulation, suggesting that it is not driven by feature repetitions. Moreover, distributional analyses revealed that the advantage for congruent trials decreased as reaction time increased similarly following congruent and incongruent trials. Finally, a large increase in RT was observed when repeated responses were made to novel stimuli and when novel responses were made to repeated stimuli. This effect also showed a sequential modulation regardless of whether the stimulus repeated. The findings suggest that, even in two-choice tasks, response selection is mediated by complex, dynamic representations that encode abstract properties of the task rather than just simple features.     

Unconscious priming of task sets: The role of spatial attention

Unconscious stimuli activate task sets, mental programs that orchestrate performance of complex tasks, but the role of attention in such effects has not been addressed. In previous studies, unconscious prime stimuli appeared at attended locations and were explicitly specified in the task instructions; spatial attention to the prime and/or a specific conscious attentional set may thus be required for such unconscious activation to arise. In the present experiments, a learning phase established associations between unconscious prime stimuli and performance of two tasks. These associations influenced task performance in a subsequent test phase, even though the primes were not specified in current task instructions. This is the first demonstration that unconscious stimuli can prime task sets independently of a current attentional set that specifies stimulus-task mappings. Such priming was not influenced by spatial attention cues, in contrast to clear attention influences in comparison trials that mimicked conditions employed by previous studies.     

Orientation sensitivity in the peripheral visual field

Orientation sensitivity in the peripheral visual field has been tested in two tasks: (a) setting horizontal the orientation of a grating at various retinal eccentricities, and (b) matching the orientation of a peripherally viewed grating as close as possible to an oblique reference viewed foveally. Both performances fall off with increasing retinal eccentricity. Magnification of the stimulus optimizes peripheral performance. Peripheral performance, optimized by magnification, varies with retinal eccentricity. It approaches, but does not reach, the foveal value (tested by the same method) at 10 deg of eccentricity, and is much lower at 20 and 30 deg of eccentricity.     

Dissociations between reaction times and temporal order judgments: a diffusion model approach

A diffusion model for simple reaction time (RT) and temporal order judgment (TOJ) tasks was developed to account for a commonly observed dissociation between these 2 tasks: Most stimulus manipulations (e.g., intensity) have larger effects in RT tasks than in TOJ tasks. The model assumes that a detection criterion determines the level of sensory evidence needed to conclude that a stimulus has been presented. Analysis of the performance that would be achieved with different possible criterion settings revealed that performance was optimal with a lower criterion setting for the TOJ task than for the RT task. In addition, the model predicts that effects of stimulus manipulations should increase with the size of the detection criterion. Thus, the model suggests that commonly observed dissociations between RT and TOJ tasks may simply be due to performance optimization in the face of conflicting task demands.     

Object-based and egocentric mental rotation performance in older adults: The importance of gender differences and motor ability

In this study, mental rotation performance was assessed in both an object-based task, human figures and letters as stimuli, and in an egocentric-based task, a human figure as a stimulus, in 60 older persons between 60 and 71 years old (30 women, 30 men). Additionally all participants completed three motor tests measuring balance and mobility. The results show that the reaction time was slower for letters than for both human figure tasks and the mental rotation speed was faster over all for egocentric mental rotation tasks. Gender differences were found in the accuracy measurement, favoring males, and were independent of stimulus type, kind of transformation, and angular disparity. Furthermore, a regression analysis showed that the accuracy rate for object-based transformations with body stimuli could be predicted by gender and balance ability. This study showed that the mental rotation performance in older adults depends on stimulus type, kind of transformation, and gender and that performance partially relates to motor ability.     

Effects of image background on spatial-frequency thresholds for face recognition

A great deal of work has been devoted to the question of which spatial frequencies, if any, are optimal for various visual tasks, such as face and object recognition. However, to date these studies have all been carried out with stimuli set against a uniform background. It is possible that this type of stimulus does not produce ecologically valid results. The natural world in which visual tasks normally take place involves a great deal of luminance variation and distracting visual structure, which may alter the spatial frequencies necessary for a task. We conducted two experiments that examined the effects of image background on the spatial-frequency thresholds (50% maximum of a low-pass or high-pass Butterworth filter) for face recognition by the psychophysical methods of adjustment and constant stimuli. In both experiments we found no significant difference in spatial-frequency thresholds between uniform-grey backgrounds and natural-scene backgrounds, and only minor differences between uniform-grey backgrounds and fractal noise backgrounds. This suggests that results obtained with uniform backgrounds are ecologically valid and that background effects, if they exist, are small.     

Interactions between view changes and shape changes in picture-picture matching

Four experiments are reported in which pictures of different morphs of novel, complex, 3-D objects, similar to objects which we must identify in the real world, were presented. We investigated how changes of viewpoint influence our ability to discriminate between morphs. View changes had a powerful effect on performance in picture-picture matching tasks when similarly shaped morphs had to be discriminated. Shape changes were detected faster and more accurately when morphs were depicted from the same rather than different views. In contrast, view change had no effect when dissimilarly shaped morphs had to be discriminated. This interaction between the effects of view change and shape change was found both for simultaneous stimulus presentation and for sequential presentation with interstimulus intervals up to 3600 ms. The interaction was found after repeated presentations of the stimuli before the matching task and after practice at the matching task as well as after no such pre-exposure to the stimuli or to the task. The results demonstrate the difficulty in activating abstract, view-insensitive representations to help to achieve object constancy, even when matching over long interstimulus intervals or after stimuli have already been seen many times.     

Effects of Image Preprocessing on Face Matching and Recognition in Human Observers

In person identification, recognition failure due to variations of illumination is common. In this study, we employed image‐processing techniques to tackle this problem. Participants performed recognition and matching tasks where the face stimuli were either original images or computer‐processed images in which shading was weakened via a number of image‐processing techniques. The results show that whereas recognition accuracy in a memory task was unaffected, some of the techniques significantly improved the identification performance in a face‐matching task. We conclude that relative to long‐term face memory, face matching is more susceptible to discrepancy of shading in different images of a face. Reducing the discrepancy by certain preprocessing techniques can facilitate person identification when original face images contain large illumination differences. Copyright © 2013 John Wiley & Sons, Ltd.     

The influence of cue-task association and location on switch cost and alternating-switch cost.

Task-switching performance is strongly influenced by whether the imperative stimulus uniquely specifies which task to perform: Switch cost is substantial with bivalent stimuli but is greatly reduced with univalent stimuli, suggesting that available contextual information influences processing in task-switching situations. The present study examined whether task-relevant information provided by task cues influences the magnitude of switch cost in a parallel manner. Cues presented 500 ms prior to a trivalent stimulus indicated which of three tasks to perform. These cues either had a preexisting association with the to-be-performed task (verbal cues), or a recently learned association with the task (spatial and shape cues). The results paralleled the effects of stimulus bivalence: substantial switch cost with recently learned cue-task associations and greatly reduced switch cost with preexisting cue-task associations. This suggests that both stimulus-based and cue-based information can activate the relevant task set, possibly providing external support to endogenous control processes. Alternating-switch cost, a greater cost for switching back to a recently abandoned task, was also observed with both preexisting and recently learned cue-task associations, but only when all tasks were presented in a consistent spatial location. When spatial location was used to cue the to-be-performed tasks, no alternating-switch cost was observed, suggesting that different processes may be involved when tasks are uniquely located in space. Specification of the nature of these processes may prove to be complex, as post-hoc inspection of the data suggested that for the spatial cue condition, the alternating-switch cost may oscillate between cost and benefit, depending on the relevant task.     

Establishing Arbitrary Stimulus Classes via Identity-matching Training and Non-reinforced Matching with Complex Stimuli

The present study investigated whether training on an identity match-to-sample task followed by non-reinforced matching probes with complex stimuli leads to the emergence of multiple arbitrary matching performances and arbitrary stimulus classes in preschool children. In Experiment 1, eight subjects were trained on a colour-matching task (A-A). Then they received tests with complex AB and AC colour-form stimuli (AB-A, B-AB; AC-A, C-AC). These tasks were designed to help subjects respond to both elements of each complex stimulus. Subsequent B-A, C-A, A-B, A-C, B-C, and C-B tests revealed that all subjects had acquired class-consistent colour-form and form-form relations. Experiment 2 examined whether these results could be replicated when subjects were encouraged to respond to the colour elements of some (AB) complex stimuli and to the form elements of other (AC) stimuli. The procedures were the same as in Experiment 1 except that during the first test only A-AB and C-AC tasks were used. Six of eight subjects demonstrated all tested relations.