Perceptual strength is different from sensorimotor strength: Evidence from the centre–periphery asymmetry in masked priming

Near-threshold prime stimuli can facilitate or hinder responses to target stimuli, creating either a positive compatibility effect (PCE) or a negative compatibility effect (NCE). An asymmetry has been reported between primes presented in near periphery, which produced a PCE, and foveal primes, which produced an NCE under comparable conditions. This asymmetry has been attributed to the difference in retinal sensitivity, but it remains unclear whether this means that equating discrimination performance for primes in fovea and periphery, in order to account for differences in perceptual sensitivity, would make the priming effects the same. Wider work indicates that perceptual ability can dissociate from visuomotor effects, predicting that equating perceptual ability for fovea and periphery would not equate priming. We tested these opposite possibilities by matching discrimination performance for masked Gabor patches in fovea and near periphery (6°) and using these as primes in a masked priming paradigm expected to elicit NCEs. We found the asymmetry remained: NCE for fovea and PCE for periphery. We replicated this with both blocked and randomized procedures to check for attentional effects. We conclude that equating perceptual strength (discriminability) of stimuli does not equate their sensorimotor impact due to differences in the relative importance of different visual pathways and differing temporal dynamics in perceptual and sensorimotor processes.     

Peripheral and foveal segmentation of angle textures

Studies of the effects of retinal eccentricity on the visual segmentation of textures are presented. The textures used in these studies were composed of angle elements. These were presented tachistoscopically to college students in three different experiments. Results showed that there were different relationships between segmentation performance and eccentricity, depending on the width of the angles used in the background and target texture. One major difference was that peak performance was found in the fovea in some conditions, and in peripheral areas in other conditions. Performance in the fovea and the periphery seemed to be determined by qualitatively different features. It was assumed that an appropriate explanation is that the system-internal representation of a specific stimulus within the early visual system differs as a function of the retinal location at which it is projected. Thus, the critical features discriminating between target and background texture have to be sought in the system-internal representation of the stimulus instead of in the stimulus itself. The data show that a relatively exact system-internal representation of the stimulus is present in the fovea, where performance is determined by angle width. In the periphery, in contrast, angles seem to be represented as “blobs,” and performance is determined by the orientation of the blobs’ main axes.     

Retinal location and its effect on the processing of target and distractor information

Two experiments were conducted to study the perceptual facilitation and inhibition that occurs between foveal and parafoveal or peripheral regions of the eye. Experiment 1 used a Stroop task to compare color detection latencies of foveal and parafoveal targets. The target and distractor components of the Stroop stimuli were separated and presented with varied stimulus onset asynchronies. Experiment 2 used a Stroop-like task to replicate and extend the findings into the visual periphery. Subjects were found to process foveally presented distractor information while attending to targets presented in parafoveal or peripheral regions of the eye. Distractor information that was incompatible was suppressed while compatible information was used to facilitate target processing. When the targets were presented foveally along with the distractor information, subjects appeared to automatically process the distractor information. The findings are discussed within the framework of past studies that presented subjects with competing tasks across retinal location. The implications of these findings to a two-process theory of attention are also considered.     

Brightness and retinal locus: Effects of target size and spectral composition

Ss gave numerical estimates of brightness for stimuli presented to the foveal and peripheral retina. Experiment 1 showed that the periphery’s superior sensitivity to white light is relatively independent of target size. Experiment 2 showed that the periphery is more sensitive than the fovea to violet light, but is less sensitive than the fovea to red light. These results are explicable in terms of differences between rod and cone mediation of brightness.     

Naming fluency in dyslexic and nondyslexic readers: Differential effects of visual crowding in foveal,parafoveal, and peripheral vision

Reading fluency is often indexed by performance on rapid automatized naming (RAN) tasks, which are known to reflect speed of access to lexical codes. We used eye tracking to investigate visual influences on naming fluency. Specifically, we examined how visual crowding affects fluency in a RAN-letters task on an item-by-item basis, by systematically manipulating the interletter spacing of items, such that upcoming letters in the array were viewed in the fovea, parafovea, or periphery relative to a given fixated letter. All lexical information was kept constant. Nondyslexic readers’ gaze durations were longer in foveal than in parafoveal and peripheral trials, indicating that visual crowding slows processing even for fluent readers. Dyslexics’ gaze durations were longer in foveal and parafoveal trials than in peripheral trials. Our results suggest that for dyslexic readers, influences of crowding on naming speed extend to a broader visual span (to parafoveal vision) than that for nondyslexic readers, but do not extend as far as peripheral vision. The findings extend previous research by elucidating the different visual spans within which crowding operates for dyslexic and nondyslexic readers in an online fluency task.     

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.     

The relative benefit of word context is a constant proportion of letter identification time

Letter identification is reduced when the target letter is surrounded by other, flanking letters. This visual crowding is known to be impacted by physical changes to the target and flanks, such as spatial frequency content, polarity, and interletter spacing. There is also evidence that visual crowding is reduced when the flanking letters and the target letter form a word. The research reported here investigated whether these two phenomena are independent of each other or whether the degree of visual crowding impacts the benefit of word context. Stimulus duration thresholds for letters presented alone and for the middle letters of 3-letter words and nonwords were determined for stimuli presented at the fovea and at the periphery. In Experiment 1, the benefit of word context was found to be the same at the fovea, where visual crowding is minimal, and at the periphery, where visual crowding is substantial. In Experiment 2, visual crowding was manipulated by changing the interletter spacing. Here, too, the benefit of word context was fairly constant for the two retinal locations (fovea or periphery), as well as with changes in interletter spacing. These data call into question both the idea that the benefit of word context is greater when stimulus quality is reduced (as is the case with visual crowding) and the idea that words are processed more effectively when they are presented at the fovea.     

Brightness as a function of retinal locus

Brightness functions were determined for the dark-adapted fovea and periphery. In one series of experiments, observers matched numbers to the brightness of a 1° white target at various intensities, presented half the time to the fovea, the other half to one of five peripheral loci: 5°, 12°, 20°, 35°, and 60°. In a second series, observers matched the brightness of a 1° white target in the fovea of one eye to the brightness of an identical target in the periphery of the other eye at various intensities. Thresholds were also determined for the fovea and for the five peripheral loci by a staircase procedure. The magnitude estimations and the interocular matches concur in showing that a stimulus of fixed luminance appears brighter in the periphery than in the fovea. The brightness was found to be maximal at 20°. Brightness grows as a similar power function of luminance at all six retinal positions.     

Brightness as a function of retinal locus

Brightness functions were determined for the dark-adapted fovea and periphery. In one series of experiments, observers matched numbers to the brightness of a 1° white target at various intensities, presented half the time to the fovea, the other half to one of five peripheral loci: 5°, 12°, 20°, 35°, and 60°. In a second series, observers matched the brightness of a 1° white target in the fovea of one eye to the brightness of an identical target in the periphery of the other eye at various intensities. Thresholds were also determined for the fovea and for the five peripheral loci by a staircase procedure. The magnitude estimations and the interocular matches concur in showing that a stimulus of fixed luminance appears brighter in the periphery than in the fovea. The brightness was found to be maximal at 20°. Brightness grows as a similar power function of luminance at all six retinal positions.     

Peripheral visual processing

An attempt was made to examine the development of the ability to identify stimuli presented to peripheral vision in several different tasks. Five- and 8-year-old children and college adults saw, for 20 msec, either a single figure at 1°, 2°, 4°, or 6° of visual angle from the fovea (singleform condition) or an off-foveal figure with an additional figure at the fovea (double-form condition). In the double-form conditions, the subjects were required to identify either the peripheral figure only (double-form presentation) or both figures (double-form report). The main effects of Age, Distance, and Form Condition were significant. Accuracy improved with increasing age and with decreasing distance. The Form Condition effect reflected lower accuracy in the two double-form conditions than in the single-form condition. Interestingly, there was no difference between the two double-form conditions, suggesting that the mere presence of a foveal stimulus, with instructions to ignore it, produces as much decrement in peripheral performance as when subjects are told to fully process and report the foveal stimulus. Also, there was no interaction between Form Condition and Distance, suggesting that the label “tunnel vision” may be misleading, since the presence of the foveal stimulus seems to have an equal effect on all peripheral locations and does not really “restrict” the size of the effective visual field.     

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.     

I know you are beautiful even without looking at you: discrimination of facial beauty in peripheral vision

Earlier research suggests that facial attractiveness may capture attention at parafovea. However, little is known about how well facial beauty can be detected at parafoveal and peripheral vision. Participants in this study judged relative attractiveness of a face pair presented simultaneously at several eccentricities from the central fixation. The results show that beauty is not only detectable at parafovea but also at periphery. The discrimination performance at parafovea was indistinguishable from the performance around the fovea. Moreover, performance was well above chance even at the periphery. The results show that the visual system is able to use the low-spatial-frequency information to appraise attractiveness. These findings not only provide an explanation why a beautiful face could capture attention when central vision is already engaged elsewhere, but also reveal the potential means by which a crowd of faces is quickly scanned for attractiveness.     

Retinal location and its effect on the spatial distribution of visual attention

A series of studies tested for distractor compatibility effects across wide target/distractor distances (0.6 degree to 20 degrees of visual angle). The effects of precue condition, constant/varied target location, horizontal/vertical distractor distance, and foveal/peripheral presentation were studied. Results show strong compatibility effects across wide distances when distractors are at peripheral retinal locations. When both stimuli were presented at the same peripheral location in opposite hemifields, compatibility effects were evident within an area of at least 2.5 degrees of visual angle. In contrast, when foveally placed distractors were used, compatibility effects were found primarily with target letters positioned near. The findings suggest that distance effects are not homogeneous across retinal location.     

Do deaf individuals have better visual skills in the periphery? Evidence from processing facial attributes

ABSTRACT

Studies examining visual abilities in individuals with early auditory deprivation have reached mixed conclusions, with some finding congenital auditory deprivation and/or lifelong use of a visuospatial language improves specific visual skills and others failing to find substantial differences. A more consistent finding is enhanced peripheral vision and an increased ability to efficiently distribute attention to the visual periphery following auditory deprivation. However, the extent to which this applies to visual skills in general or to certain conspicuous stimuli, such as faces, in particular is unknown. We examined the perceptual resolution of peripheral vision in the deaf, testing various facial attributes typically associated with high-resolution scrutiny of foveal information processing. We compared performance in face-identification tasks to performance using non-face control stimuli. Although we found no enhanced perceptual representations in face identification, gender categorization, or eye gaze direction recognition tasks, fearful expressions showed greater resilience than happy or neutral ones to increasing eccentricities. In the absence of an alerting sound, the visual system of auditory deprived individuals may develop greater sensitivity to specific conspicuous stimuli as a compensatory mechanism. The results also suggest neural reorganization in the deaf in their opposite advantage of the right visual field in face identification tasks.     

Letter identification and lateral masking in dyslexic and average readers

Lateral masking and letter identification in dyslexic and average readers were investigated with a methodology that corrected for some of the weaknesses of the Geiger and Lettvin studies (1986, 1987). Target letters were presented alone or embedded within three-letter arrays at retinal locations from 0 degrees to 15 degrees to the right or left of a fixation point. A foveal letter, which was the same as or different from a target letter, appeared as a distractor, and comparisons were made between scaled and unscaled stimuli. Dyslexic readers were found to be better than average readers at detecting scaled letters embedded in an array in some of the peripheral locations tested. Unlike the results of Geiger and Lettvin, however, this finding of better letter detection in the periphery by dyslexics was limited to selected conditions of the study. Reading groups were also found to differ in responding to the foveal distractor in the letter task. Detection of letters by average readers was affected by the type of distractor, but this variable was not found to influence the dyslexic readers. These findings suggest some differences between dyslexic and average readers in attention to stimuli presented at multiple locations in the visual field.     

Visual resolution in the periphery

Visual acuity thresholds were determined for two Os with a 3-deg square grating target presented for 0.2 sec within a steadily illuminated surround field matched in luminance to the test field. Measurements were made in the fovea, and at 10, 20, and 30 deg along the horizontal meridian of the temporal retina, at luminances between ?3.5 and 3.0 log mL. The foveal acuity-luminance functions showed a large increase in acuity up to 1 or 2 log mL, but at peripheral locations very little increase occurred above 0 log mL. The maximum acuity reached at photopic luminances dropped sharply with increasing eccentricity. Visual acuities were two to four times higher than those previously reported for the periphery; methodological and target differences are presented to account for this result.     

Raised visual detection thresholds depend on the level of complexity of cognitive foveal loading.

The objective of the study was to measure the interactions between visual thresholds for a simple light (the secondary task) presented peripherally and a simultaneously performed cognitive task (the primary task) presented foveally The primary task was highly visible but varied according to its cognitive complexity. Interactions between the tasks were determined by measuring detection thresholds for the peripheral task and accuracy of performance of the foveal task. Effects were measured for 5, 10, 20, and 30 deg eccentricity of the peripherally presented light and for three levels of cognitive complexity. Mesopic conditions (0.5 lx) were used. As expected, the concurrent presentation of the foveal cognitive task reduced peripheral sensitivity. Moreover, performance of the foveal task was adversely affected when conducting the peripheral task. Performance on both tasks was reduced as the level of complexity of the cognitive task increased. There were qualitative differences in task interactions between the central 10 deg and at greater eccentricities. Within 10 deg there was a disproportionate effect of eccentricity, previously interpreted as the 'tunnel-vision' model of visual field narrowing. Interactions outside 10 deg were less affected by eccentricity. These results are discussed in terms of the known neurophysiological characteristics of the primary visual pathway.     

周边视觉的知觉学习

知觉学习是指知觉能力随着知觉训练或经验逐渐改变的现象。它具有特异性-迁移性,可以根据时程划分为快速学习和慢速学习。知觉学习意味着与知觉直接对应的脑区神经元激活方式的变化,并且与注意有着一定的联系。目前周边视觉的知觉学习研究已有一些成果：对于非语词刺激,随着练习,判断目标刺激（例如刺激朝向、游标视敏度）的能力,有很大的提升;对于语词刺激,周边视觉的知觉学习可以帮助提高阅读速度。可以通过提高视觉广度来提高周边视觉的阅读速度。周边视觉的知觉学习还有着重大应用价值,可以帮助中央凹视觉缺损的人们提高周边视觉能力,帮助恢复阅读能力。     

三维空间中不同视野深度位置上的返回抑制

通过虚拟现实构建虚拟三维场景,将二维平面视觉空间返回抑制范式应用到三维空间,通过两个实验操纵了目标深度、线索有效性以及视野位置三个变量,考察注意在三维空间不同视野深度位置上进行定向/重定向产生的返回抑制效应。结果发现,(1)二次线索化位于固定的中央视野时,不论目标出现在近处空间还是出现在远处空间,外周视野条件下的返回抑制大于中央视野条件下的返回抑制;(2)二次线索化位于非固定的中央视野时,近处空间和远处空间的返回抑制存在分离,表现为当目标出现在远处空间时,外周视野条件下的返回抑制效应减小。研究表明,三维空间中外周视野深度位置上的返回抑制与中央视野深度位置上的返回抑制存在差异。     

Sources of position-perception error for small isolated targets

It has often been reported that, in the presence of static reference stimuli, briefly presented visual targets are perceived as being closer to the fixation point than they actually are. The first purpose of the present study was to investigate whether the same phenomenon can be demonstrated in a situation without static reference stimuli. Experiment 1, with position naming as the task, showed that such a central shift is also observed under these conditions. This finding is of importance because it completes an explanation for central near-location errors in the partial-report bar-probe task. The second purpose of the present study was to provide an explanation for these central shifts. For this explanation information about the exact size of the central shift is required. In Exps. 2, 3, and 4, with cursor setting as the task, it was attempted to assess more precisely the size of the central shifts. These experiments revealed that two different factors determine the results in cursor setting tasks; a factor “target position” and a factor “cursor position.” Experiment 5 showed that it is the point of fixation, not the fixation point, that serves, at least in part, as the reference point in this type of task. All the findings together allow us to conclude that the target positions are underestimated by about 10%. From vision research it is known that saccadic eye movements, performed for bringing a target in the fovea, also show an undershoot of about 10%. It is therefore concluded that the system in charge of saccadic eye movements also provides the metric in visual space within a single eye fixation. Received: 11 February 1998 / Accepted: 25 June 1998