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.     

Psychophysics of lateral tachistoscopic presentation

Human visual performance depends upon the retinal position to which a target is delivered. A general finding is that performance measured in a variety of psychophysical tasks deteriorates as a target is presented to more eccentric retinal regions. One purpose of this paper is to describe differences between foveal and peripheral vision in a number of psychophysical tasks. A second purpose is to review studies which have attempted to account for the fall off in visual performance between central and peripheral target presentations. A third purpose is to consider the contribution of the periphery to perception since targets which are sufficiently large project not only on receptors in the fovea but also on those in the periphery. In addition, stimuli presented to the peripheral retina can influence the processing of a target presented to the central retinal region. A fourth purpose is to review studies which have attempted to compensate for foveal and peripheral differences by scaling the target in size or some other attribute in proportion to the cortical magnification factor. A final purpose of this paper is to consider whether the fovea and the periphery are specialized for different functions.     

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.     

Peripheral vision: The effects of developmental,perceptual, and cognitive factors

The effects of perceptual and cognitive factors on information processing in the visual periphery were studied in 5- and 8-year-old children and in adults. Subjects judged either the similarity (Study 1) or the identity (Study 2) of geometric forms. In both studies, two forms were simultaneously presented for 20 msec at 2, 4, or 6°, with one form on either side of the fovea. Type of form and Axis of presentation were varied. Both studies demonstrated declining performance with increasing distance, poorer performance with open than closed forms, poorest performance along the vertical axis, and no major interaction of these factors with age. Greater “flattening” of the visual field was found in Study 2 than in Study 1 for all age groups. The results indicate that the parafoveal visual field is elliptical and that more difficult tasks accentuate this asymmetry. This effect of task demands on the relative flatness of the effective visual field cannot be interpreted on the basis of anatomical factors. The findings indicated striking developmental similarity in the effect of several variables on parafoveal processing and challenge the idea of greater tunnel vision in preschoolers than in adults. Further, the data suggest that perceptual and cognitive factors influence the size and shape of the effective visual field across the full age range studied.     

Reduced looming sensitivity in primary school children with Developmental Co-ordination Disorder

Almost all locomotor animals are sensitive to optical expansion (visual looming) and for most animals this sensitivity is evident very early in their development. In humans there is evidence that responses to looming stimuli begin in the first 6 weeks of life, but here we demonstrate that as children become independent their perceptual acuity needs to be 50 to 100 times better than has been demonstrated in infants in order to be skilful at collision avoidance at a roadside. We have recently established that sensitivity to the detection of visual looming in 6- to 11-year-old children is significantly below that of adults (Wann, Poulter & Purcell, 2011). Here, using comparable methods, we explore looming detection sensitivity in children with Developmental Co-ordination Disorder (DCD), who show broad patterns of impairment in visuo-motor control. We presented visual simulations of approaching vehicles, scaled to represent different approach rates, to children with DCD aged between 6 and 11 years (n = 11) and typically developing age and gender matched controls (n = 11). Looming detection thresholds were measured under foveal and perifoveal viewing conditions, for isotropic expansion and isotropic expansion with simulated viewpoint motion. Our results show that there are situations in which children with DCD may fail to detect vehicles approaching at speeds in excess of 22 km/h, suggesting a developmental immaturity in looming sensitivity. This provides one of the first clear demonstrations of low-level motion processing deficits in children with DCD. The decrement observed may give rise to potential errors in the road crossing behaviour of these children, whereby approaching vehicles could be perceived as stationary. These findings further contribute towards understanding the adverse statistic that children under 9 years of age are four times more likely than adults to be involved in a road accident as a pedestrian.     

Peripheral target recognition and visual field narrowing in aviators and nonaviators

In the two experiments that examined recognition accuracy in the near visual periphery as a function of foveal cognitive load, aviators were shown to have larger effective functional visual fields than nonaviators. The aviators appeared to be far less susceptible to the visual field narrowing found in nonaviators. The narrowing found in nonaviators suggested a tunnel-vision-like pattern. The rather small effect of load increases on aviator performance was likely due to specialized training and experience. Student aviators who averaged only 70 flight hr were clearly superior to nonaviators on peripheral recognition with a concomitant foveal task.     

The effects of onset and offset warning and post-target stimuli on the saccade latency of children and adults

Two studies, involving children (mean age = 10 years) and adults, investigated the effects of visual stimulus onsets and offsets on the latency of saccades to peripheral targets. Saccade latency was reduced when foveal stimulus onsets or offsets preceded the target. When stimulus onset occurred 100 msec after target onset, the stimulus interfered with responding, with this interference effect significantly greater for children than for adults. When stimuli were presented in the peripheral visual field facilitation and interference effects were similar for children and adults. These results were interpreted as indicating that oculomotor processes are similar in children and adults while the stimulus intake processes that follow stimulus onset at the point of fixation have a greater interference effect on children's than on adults' eye movements.     

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.     

A hazard-perception test for cycling children: An exploratory study

In car driving, hazard perception tests have revealed important differences in perceptual-cognitive skills between novice and experienced drivers. Although these insights have led to new educational programs for learner drivers, similar research has not yet been done for other road users such as bicyclists. In the current investigation, a first hazard perception test for bicyclists has been developed and tested on both adults and children of ±eight year old. The test consisted of three sections in which visual behaviour, environmental awareness, and risk perception were evaluated respectively. Although only few differences in visual behaviour and environmental awareness were found, adults were found to react earlier on hazards than children. These results suggest that children have difficulties to interpret the necessary information to react timely to hazardous traffic situations. Alternatively, the current set-up of the hazard perception test might not have been suitable to detect differences in visual behaviour between children and adults in traffic situations. Therefore the development and use of future hazard perception tests for bicyclists is discussed.     

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.     

Deaf and hearing children: a comparison of peripheral vision development

This study investigated peripheral vision (at least 30° eccentric to fixation) development in profoundly deaf children without cochlear implantation, and compared this to age-matched hearing controls as well as to deaf and hearing adult data. Deaf and hearing children between the ages of 5 and 15 years were assessed using a new, specifically paediatric designed method of static perimetry. The deaf group (N = 25) were 14 females and 11 males, mean age 9.92 years (range 5-15 years). The hearing group (N = 64) were 34 females, 30 males, mean age 9.13 years (range 5-15 years). All participants had good visual acuity in both eyes (< 0.200 LogMAR). Accuracy of detection and reaction time to briefly presented LED stimuli of three light intensities, at eccentricities between 30° and 85° were measured while fixation was maintained to a central target. The study found reduced peripheral vision in deaf children between 5 and 10 years of age. Deaf children (aged 5-10 years) showed slower reaction times to all stimuli and reduced ability to detect and accurately report dim stimuli in the far periphery. Deaf children performed equally to hearing children aged 11-12 years. Deaf adolescents aged 13-15 years demonstrated faster reaction times to all peripheral stimuli in comparison to hearing controls. Adolescent results were consistent with deaf and hearing adult performances wherein deaf adults also showed significantly faster reaction times than hearing controls. Peripheral vision performance on this task was found to reach adult-like levels of maturity in deaf and hearing children, both in reaction time and accuracy of detection at the age of 11-12 years.     

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.     

The effect of spatial order on piecemeal shape recognition: A developmental study

Stationary shapes were displayed piecemeal by moving an aperture from one place to another around their contours. Shape recognition was poorer with an unpredictable order of display. This result is more consistent with hypothesis-testing than with either eye-movement or visual information models of shape recognition. Shape recognition was poorer for 9- and 11-year-old children than for adults.     

Spoken word recognition by young children and adults

The nature of the stimulus information that is important for the recognition of auditorily presented words by young (5-year-old) children and adults was studied. In Experiment 1, subjects identified and rated the extent of noise disruption for words in which white noise either was added to or replaced phoneme (fricative and nonfricative) segments in word-initial, -medial or -final position. In Experiment 2, subjects identified words as acoustic-phonetic information accumulated either from their beginnings or ends with silence or envelope-shaped noise replacing the nonpresented parts. The results point to developmental similarities in the derivation of phoneme identities from impoverished sensory input to support the component processes of recognition. However, position-specific information may play a less prominent role in recognition for children than for adults.     

Facial expression recognition in peripheral versus central vision: role of the eyes and the mouth

This study investigated facial expression recognition in peripheral relative to central vision, and the factors accounting for the recognition advantage of some expressions in the visual periphery. Whole faces or only the eyes or the mouth regions were presented for 150 ms, either at fixation or extrafoveally (2.5° or 6°), followed by a backward mask and a probe word. Results indicated that (a) all the basic expressions were recognized above chance level, although performance in peripheral vision was less impaired for happy than for non-happy expressions, (b) the happy face advantage remained when only the mouth region was presented, and (c) the smiling mouth was the most visually salient and most distinctive facial feature of all expressions. This suggests that the saliency and the diagnostic value of the smile account for the advantage in happy face recognition in peripheral vision. Because of saliency, the smiling mouth accrues sensory gain and becomes resistant to visual degradation due to stimulus eccentricity, thus remaining accessible extrafoveally. Because of diagnostic value, the smile provides a distinctive single cue of facial happiness, thus bypassing integration of face parts and reducing susceptibility to breakdown of configural processing in peripheral vision.     

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.     

Focal attention and the perception of pattern structure in extrafoveal vision

Several studies have shown that visual attention enhances the encoding of the positional relationships between pattern elements, i.e., the perception of pattern structure. This theoretical note discusses the possibility that the inferiority of extrafoveal vision in the perception of pattern structure results, at least partially, from less effective focal attention in the periphery. Hence, there may exist higher level differences between foveal and extrafoveal vision in information processing which cannot be explained by the spatial inhomogeneity of the retino-striate system.     

Age differences in peripheral letter perception

The capacities of 96 eight- and nine-year-old children and 96 adults to discriminate letters in the visual periphery were tested. Four-letter arrays were presented at the fixation point or centered 4 degrees to the left or right. Threshold exposure durations were estimated by a method of ascending limits. Analyses of a transformed threshold measure revealed that although children were less able than adults to discriminate letters in all positions, age differences were greatest for peripherally presented arrays. Development specific to the peripheral visual systems seems implicated.     

Detection of emotional faces: low perceptual threshold and wide attentional span

In two experiments, prime face stimuli with an emotional or a neutral expression were presented individually for 25 to 125 ms, either in foveal or parafoveal vision; following a mask, a probe face or a word label appeared for recognition. Accurate detection and sensitivity (A') were higher for angry, happy, and sad faces than for nonemotional (neutral) or novel (scheming) faces at short exposure times (25-75 ms), in both the foveal and the parafoveal field, and with both the probe face and the probe word. These results indicate that there is a low perceptual threshold for unambiguous emotional faces, which are especially likely to be detected both within and outside the focus of attention; and that this facilitated detection involves processing of the affective meaning of faces, not only discrimination of formal visual features.     

Higher face recognition ability in girls: Magnified by own-sex and own-ethnicity bias

Earlier studies on adults have shown sex differences in face recognition. Women tend to recognise more faces of other women than men do, whereas there are no sex differences with regard to male faces. In order to test the generality of earlier findings and to examine potential reasons for the observed pattern of sex differences, two groups of Swedish 9-year-old children (n = 101 and n = 96) viewed faces of either Swedish or Bangladeshi children and adults for later recognition. Results showed that girls outperformed boys in recognition of female faces, irrespective of ethnicity and age of the faces. Boys and girls recognised Swedish male faces to an equal extent, whereas girls recognised more Bangladeshi male faces than boys did. These results indicate that three factors explain the magnitude of sex differences in face recognition: an overall female superior face recognition ability, the correspondence between the sex of viewer and the gender of the face, and prior knowledge of the ethnicity of the face.