Perceptual learning and attention: Reduction of object attention limitations with practice

Perceptual learning has widely been claimed to be attention driven; attention assists in choosing the relevant sensory information and attention may be necessary in many cases for learning. In this paper, we focus on the interaction of perceptual learning and attention - that perceptual learning can reduce or eliminate the limitations of attention, or, correspondingly, that perceptual learning depends on the attention condition. Object attention is a robust limit on performance. Two attributes of a single attended object may be reported without loss, while the same two attributes of different objects can exhibit a substantial dual-report deficit due to the sharing of attention between objects. The current experiments document that this fundamental dual-object report deficit can be reduced, or eliminated, through perceptual learning that is partially specific to retinal location. This suggests that alternative routes established by practice may reduce the competition between objects for processing resources.     

Perceptual learning of highly demanding visual search tasks

Inefficient visual search can become efficient with practice [Vision Research 35 (1995) 2037; 40 (2000) 2925]. In this study, we wondered whether this improvement depends on unique visual features associated with the target, on differences in item-specific brightness distribution between target and distractors, or only on a change in the allocation of attention and thus global search strategy. We found that both, unique visual features and differences in brightness distribution lead to parallelisation with practice of originally inefficient search. Prolonged practice of inefficient search tasks lacking both unique visual features and differences in brightness distribution (conjunctions) does not lead to improved performance, thus indicating that perceptual learning in visual search does not solely reflect an unspecific global improvement in search strategy. Changing the brightness polarity of the stimuli leads to instantaneous, complete transfer to the new task. There is no transfer but rather trade-off between the learning based on unique visual features or on differences in brightness distribution between target and distractors.     

A binocular perimetry study of the causes and implications of sensory eye dominance

Sensory eye dominance (SED) reflects an imbalance of interocular inhibition in the binocular network. Extending an earlier work (Ooi & He, 2001) that measured global SED within the central 6°, the current study measured SED locally at 17 locations within the central 8° of the binocular visual field. The eccentricities (radius) chosen for this, “binocular perimetry”, study were 0° (fovea), 2° and 4°. At each eccentricity, eight concentric locations (polar angle: 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°) were tested. The outcome, an SED map, sets up comparison between local SED and other visual functions [monocular contrast threshold, binocular disparity threshold, reaction time to detect depth, the dynamics of binocular rivalry and motor eye dominance]. Our analysis shows that an observer’s SED varies gradually across the binocular visual field both in its sign and magnitude. The strong eye channel revealed in the SED measurement does not always have a lower monocular contrast threshold, and does not need to be the motor dominant eye. There exists significant correlation between SED and binocular disparity threshold, and between SED and the response time to detect depth of a random-dot stereogram. A significant correlation is also found between SED and the eye that predominates when viewing an extended duration binocular rivalry stimulus. While it is difficult to attribute casual factors based on correlation analyses, these observations agree with the notion that an imbalance of interocular inhibition, which is largely revealed as SED, is a significant factor impeding binocular visual perception.     

A binocular perimetry study of the causes and implications of sensory eye dominance

Sensory eye dominance (SED) reflects an imbalance of interocular inhibition in the binocular network. Extending an earlier work (Ooi & He, 2001) that measured global SED within the central 6°, the current study measured SED locally at 17 locations within the central 8° of the binocular visual field. The eccentricities (radius) chosen for this, "binocular perimetry", study were 0° (fovea), 2° and 4°. At each eccentricity, eight concentric locations (polar angle: 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°) were tested. The outcome, an SED map, sets up comparison between local SED and other visual functions [monocular contrast threshold, binocular disparity threshold, reaction time to detect depth, the dynamics of binocular rivalry and motor eye dominance]. Our analysis shows that an observer's SED varies gradually across the binocular visual field both in its sign and magnitude. The strong eye channel revealed in the SED measurement does not always have a lower monocular contrast threshold, and does not need to be the motor dominant eye. There exists significant correlation between SED and binocular disparity threshold, and between SED and the response time to detect depth of a random-dot stereogram. A significant correlation is also found between SED and the eye that predominates when viewing an extended duration binocular rivalry stimulus. While it is difficult to attribute casual factors based on correlation analyses, these observations agree with the notion that an imbalance of interocular inhibition, which is largely revealed as SED, is a significant factor impeding binocular visual perception.     

Depth of focus,eye size and visual acuity

We develop formulas for calculating the approximate depth of focus of any eye. They show that the magnitude of depth of focus is inversely proportional to the size of the eye and to its visual acuity. One particular implication of these quantitative relations, which is supported by previous data from rats and human infants, is that small eyes with low acuity should have large depths of focus. We show that the observed relation between defocus and contrast sensitivity in rats in predicted by our formulas. We also analyze recent findings in human infants and show that they demonstrate a good correspondence between the improvement in accuracy of the accommodative response with age and the reduction in depth of focus (predicted from our formulas) as acuity and eye size increase over the same age range. Optical factors such as astigmatism, refractive error and chromatic and spherical aberration should have no effect on visual resolution unless they exceed the depth of focus of an eye. Thus, our arguments imply that these factors may be relatively unimportant in small eyes with low acuity.     

Perceptual learning, aging, and improved visual performance in early stages of visual processing

In the present study, we examined whether perceptual learning methods can be used to improve performance of older individuals. Subjects performed a texture discrimination task in the peripheral visual field and a letter discrimination task in central vision. The SOA threshold was derived by presenting a mask following the stimuli. Older subjects (age greater than 65 years) were either trained for 2 days using near threshold stimuli (experimental group) or were trained with the task with supra-threshold stimuli (older control group). The experimental group showed significant improvement in the task as a result of training whereas the older control group showed no significant improvement. The improved performance post-training equaled that of a younger control group and was maintained for at least 3 months. The results of two additional experiments indicate that the improved performance was not due to changes in divided attention, that the effect of perceptual learning was location specific, and that the pattern of learning was similar to that of younger subjects. These results indicate that perceptual learning with near threshold training can be used to improve visual performance among older individuals, that the improvements are not the result of practice with the visual task, and that the improvements do not transfer to non-trained locations.     

The role of the attention focus in the visual information processing underlying saccadic adaptation

Three experiments were performed to determine how an error signal for driving saccadic adaptation is derived from visual information processing. The first experiment demonstrated that an intrasaccadic displacement of a visual background does not influence saccadic adaptation when a small foveal target is used. The second experiment showed that when a different type of target, a 4.8 deg annulus, is used an intrasaccadic background shift influences the adaptive process. The third experiment showed that the size of the saccade target determines the size of the attention focus around the time of a saccade. These findings suggest that the attention focus selects the visual information used for a trans-saccadic comparison in order to generate the error signal.     

The absence of lateral congruency between sighting dominance and the eye with better visual acuity

The notion that in subjects with normal binocular vision (i.e. non-strabismic cases) the eye showing sighting dominance will also most likely be that individual's better-sighted eye has proved to be persistent. A review and analysis of the literature has now demonstrated, across several population groups, the fallacy of this belief. In fact, the occurrence of lateral congruency between sighting dominance and the eye with better visual acuity is at a statistical level no greater than chance would predict. Some clinical implications of this outcome are considered.     

视知觉学习与注意力的关系

随着人们对弱视本质以及大脑神经可塑性研究的深入,视知觉学习的概念被逐渐引入到弱视研究领域。由于视知觉学习过程中可能涉及到注意力机制,而且先前的研究显示二者之间存在相互作用。为进一步认识视知觉学习的本质,从认知神经科学和心理物理学的角度对视知觉学习与注意力关系进行综述,如弱视的视觉缺陷表现形式与发病部位、视知觉学习的特点和机制、注意力在视知觉学习中的作用及视知觉学习对注意力的影响。     

Perceptual learning of Gabor orientation identification in visual periphery: complete inter-ocular transfer of learning mechanisms

We combined the external noise paradigm, the Perceptual Template Model approach, and transfer tests to investigate the mechanisms and eye-specificity of perceptual learning of Gabor orientation in visual periphery. Coupled with a fixation task, discriminating a 5 from an S in a rapid small character string at fixation, contrast thresholds were estimated for each of eight external noise levels at two performance criteria using 3/1 and 2/1 staircases. Perceptual learning in one eye was measured over 10 practice sessions, followed by five sessions of practice in the new eye to assess transfer. We found that monocular learning improved performance (reduced contrast thresholds) with virtually equal magnitude across a wide range of external noise levels with no significant change in central task performance. Based on measurements of learning effects at two performance criterion levels, we identified a mixture of stimulus enhancement and external noise exclusion as the mechanism of perceptual learning underlying the observed improvements. Perceptual learning in the trained eye generalized completely to the untrained eye. We related the transfer patterns to known physiology and psychophysics on orientation direction coding.     

The eye movements of dyslexic children during reading and visual search: impact of the visual attention span

The eye movements of 14 French dyslexic children having a VA span reduction and 14 normal readers were compared in two tasks of visual search and text reading. The dyslexic participants made a higher number of rightward fixations in reading only. They simultaneously processed the same low number of letters in both tasks whereas normal readers processed far more letters in reading. Importantly, the children's VA span abilities related to the number of letters simultaneously processed in reading. The atypical eye movements of some dyslexic readers in reading thus appear to reflect difficulties to increase their VA span according to the task request.     

Absence of binocular summation, eye dominance, and learning effects in color discrimination

We evaluated binocular summation, eye dominance, and learning in the Trivector and Ellipses procedures of the Cambridge Colour Test (CCT). Subjects (n = 36, 18-30 years old) were recruited among students and staff from the University of S?o Paulo. Inclusion criteria were absence of ophthalmological complaints and best-corrected Snellen VA 20/20 or better. The subjects were tested in three randomly selected eye conditions: binocular, monocular dominant eye, and nondominant eye. Results obtained in the binocular and monocular conditions did not differ statistically for thresholds measured along the protan, deutan, and tritan confusion axes (ANOVA, P > 0.05). No statistical difference was detected among discrimination ellipses obtained in binocular or monocular conditions (ANOVA, P > 0.05), suggesting absence of binocular summation or of an effect of eye dominance. Possible effects of learning were examined by comparing successive thresholds obtained in the three testing conditions. There was no evidence of improvement as a function of testing order (ANCOVA, P > 0.05). We conclude that CCT thresholds are not affected by binocularity, eye dominance, or learning. Our results differ from those found by Verriest et al. (1982) using the Farnsworth-Munsell 100 Hue test and Hovis et al. (2004) using the Farnsworth-Munsell panel D-15 test.     

Use of a sustained visual attention task to determine children at risk for learning problems

Use of a sustained visual attention task to determine children "at risk" for learning problems. The purpose in the study was to compare the sustained visual attention performance of 42 first grade children on a 9.5 minute continuous performance test, as measured by error rate and off-task visual behaviors, e.g., off-task looking time and number of fixations off the task, with a measure of impulsivity and a teacher rating scale of classroom behavior designed to identify children with potential learning disabilities. The present findings suggest that the measurement of "off-task looking time" and "off-task fixations" during a sustained visual attention test are significantly related to the classroom teacher's observation of personal-social behavior and the child's decision making style. This approach for measuring sustained attention has potential use as a clinical tool in identifying and monitoring treatment methodologies for children considered "at risk" for attention and learning problems.     

The spatial profile of the focus of attention in visual search: Insights from MEG recordings

The spatial focus of attention has been suggested to resemble a spotlight, a zoom-lens, a simple gradient, or even a more complex center-surround profile. Here we review evidence from neuromagnetic recordings indicating that the spatial profile is not fixed but depends on the particular perceptual demands of the attention task. We show that visual search requiring spatial scrutiny for target discrimination produces a zone of neural attenuation in the target’s immediate surround, whereas search permitting target discrimination without spatial scrutiny is associated with a simple gradient. We provide new evidence indicating that increasing the demands on target discrimination without changing the spatial scale of discrimination does not influence surround attenuation, and that surround attenuation is also not influenced by the type of features involved in forward processing, that is whether the target location is defined by color or luminance contrast in visual search. An assessment of the time-course of attentional selection reveals that, when present, surround attenuation onsets with a substantial delay relative to the initial feed-forward sweep of processing in the visual system. The reported observations together suggest that the more complex center-surround profile arises as a consequence of top-down attentional selection in the visual system. The reviewed neuromagnetic evidence is discussed with respect to key notions of the Selective Tuning model of visual attention for which strong support is provided.     

关注干眼患者的心理问题

干眼是最常见的眼表疾病，长期慢性眼表疼痛、刺激感、视疲劳等症状严重影响患者的生活质量。部分患者对治疗失去信心、对工作和生活缺乏热情，流行病学研究显示干眼与焦虑、抑郁具有明显的相关性。干眼的积极治疗有利于患者抑郁状态的缓解，而有效的抑郁治疗又有助于干眼症状的缓解，因此眼科医生应关注干眼相关抑郁、焦虑等心理障碍的类型、机制及预防治疗措施。     

颅咽管瘤患者的视功能损害研究

目的探讨颅咽管肿瘤患者视功能检查的重要意义及眼科医生对于颅咽管瘤患者的早期诊断的重要性。方法回顾性分析2010．7—2013．6在我院南区神经外科手术证实的73名颅咽管瘤患者的临床资料包括术前的视力、视野检查结果。结果73名颅咽管瘤患者男女比例一致,41—60岁患者所占比例最高。52％患者首发症状为视功能障碍,视力下降的患者中有71％双眼视力均低于0.3。偏盲性视野占68．6％。结论重视颅咽管瘤患者的视功能损害情况,有助于眼科医生早期诊断颅咽管瘤,有助于神经外科医生的术前、术后评估,达到控制肿瘤、降低复发率的目的。     

The use of visual search to assess attention

Background: Under some conditions, the time required for a visual search increases with the number of elements to be searched. It has been suggested that the overall search time reflects the duration that attention is devoted to each element multiplied by the number of elements. On this basis, it has been proposed that visual search time can be used as a measure of attention capability in dyslexic readers. However, there is evidence to suggest that the search time reflects task difficulty rather than attentional factors. Many dyslexic readers suffer from various sensory deficits. These deficits would effectively increase task difficulty for these readers. Here we use computer simulations to investigate the potential effects of sensory deficits on visual search. Method: Visual search was modelled on a computer within the framework of signal detection theory as a matter of detecting a noisy signal from a series of noisy distractors. Sensory deficits were modelled as decreased discriminability. Results: Consistent with previous observations, we find that discriminability, which decreases with the number of distractors, may have a substantial effect on the search time. With regard to the effects of sensory deficits, we find that under low discriminability conditions, small sensory deficits may cause pronounced increases in search time. Conclusion: The finding that small sensory deficits may cause pronounced increases in search time makes it specifically problematic to use visual search to test attention in individuals who suffer from sensory deficits. This applies particularly to dyslexic individuals, many of whom have been shown to suffer from visual deficiencies.