Dorsal stream deficits suggest hidden dyslexia among deaf poor readers: correlated evidence from reduced perceptual speed and elevated coherent motion detection thresholds

Prelingual deafness and developmental dyslexia have confounding developmental effects on reading acquisition. Therefore, standard reading assessment methods for diagnosing dyslexia in hearing people are ineffective for use with deaf people. Recently, Samar, Parasnis, and Berent (2002) reported visual evoked potential evidence that deaf poor readers, compared to deaf good readers, have dorsal stream visual system deficits like those previously found for hearing dyslexics. Here, we report new psychometric and psychophysical evidence that deficits in dorsal stream function, likely involving extrastriate area MT, are associated with relatively poor reading comprehension in deaf adults. Poorer reading comprehension within a group of 23 prelingually deaf adults was associated with lower scores on the Symbol Digit Modality Test, a perceptual speed test commonly used to help identify dyslexia in hearing people. Furthermore, coherent dot motion detection thresholds, which reflect the functional status of area MT, correlated negatively with reading scores in each visual quadrant. Elevated motion thresholds for deaf poor readers were not due to general cognitive differences in IQ but were specifically correlated with poor perceptual speed. With IQ controlled, a highly reliable right visual field advantage for coherent motion detection was found. Additional analyses suggested that the functional status of dorsal stream motion detection mechanisms in deaf people is related to reading comprehension, but the direction and strength of lateralization of those mechanisms is independent of reading comprehension. Our results generally imply that dyslexia is a hidden contributor to relatively poor reading skill within the deaf population and that assessment of dorsal stream function may provide a diagnostic biological marker for dyslexia in deaf people.     

Transitive responding in hooded crows requires linearly ordered stimuli

Eight crows were taught to discriminate overlapping pairs of visual stimuli (A+ B-, B+ C-, C+ D-, and D+ E-). For 4 birds, the stimuli were colored cards with a circle of the same color on the reverse side whose diameter decreased from A to E (ordered feedback group). These circles were made available for comparison to potentially help the crows order the stimuli along a physical dimension. For the other 4 birds, the circles corresponding to the colored cards had the same diameter (constant feedback group). In later testing, a novel choice pair (BD) was presented. Reinforcement history involving stimuli B and D was controlled so that the reinforcement/nonreinforcement ratios for the latter would be greater than for the former. If, during the BD test, the crows chose between stimuli according to these reinforcement/nonreinforcement ratios, then they should prefer D; if they chose according to the diameter of the feedback stimuli, then they should prefer B. In the ordered feedback group, the crows strongly preferred B over D; in the constant feedback group, the crows' choice did not differ significantly from chance. These results, plus simulations using associative models, suggest that the orderability of the postchoice feedback stimuli is important for crows' transitive responding.     

The "what" and "where" of object representations in infancy

Four-month-olds' memory for surface feature and location information was tested following brief occlusions. When the target objects were images of female faces or monochromatic asterisks infants showed increased looking times following a change in identity or color but not following a change in location or combinations of feature and location information. When the target objects were images of manipulable toys, the infants showed increased looking times following a change in location but not identity or the binding of location and identity information. This evidence is consistent with the idea that young infants are unable to maintain the information processed separately in both the dorsal and ventral visual streams during occlusions. Our results suggest that it is the target's affordance for action that determines whether the dorsal or ventral information is selectively maintained during occlusion.     

Global and local covert visual attention: Evidence from a bayesian hidden markov model

Psychological, psychophysical and physiological research indicates that people switch between two covert attention states, local and global attention, while visually exploring complex scenes. The focus in the local attention state is on specific aspects and details of the scene, and on examining its content with greater visual detail. The focus in the global attention state is on exploring the informative and perceptually salient areas of the scene, and possibly on integrating the information contained therein. The existence of these two visual attention states, their relative prevalence and sequence in time has remained empirically untested to date. To fill this gap, we develop a psychometric model of visual covert attention that extends recent work on hidden Markov models, and we test it using eye-movement data. The model aims to describe the observed time series of saccades typically collected in eye-movement research by assuming a latent Markov process, indicative of the brain switching between global and local covert attention. We allow subjects to be in either state while exploring a stimulus visually, and to switch between them an arbitrary number of times. We relax the no-memory-property of the Markov chain. The model that we develop is estimated with MCMC methodology and calibrated on eye-movement data collected in a study of consumers' attention to print advertisements in magazines.We thank Dominique Claessens of Verify International for making the data available to us.     

Cognitive processing in literate and illiterate subjects: a review of some recent behavioral and functional neuroimaging data

The study of illiterate subjects, which for specific socio-cultural reasons did not have the opportunity to acquire basic reading and writing skills, represents one approach to study the interaction between neurobiological and cultural factors in cognitive development and the functional organization of the human brain. In addition the naturally occurring illiteracy may serve as a model for studying the influence of alphabetic orthography on auditory-verbal language. In this paper we have reviewed some recent behavioral and functional neuroimaging data indicating that learning an alphabetic written language modulates the auditory-verbal language system in a non-trivial way and provided support for the hypothesis that the functional architecture of the brain is modulated by literacy. We have also indicated that the effects of literacy and formal schooling is not limited to language related skills but appears to affect also other cognitive domains. In particular, we indicate that formal schooling influences 2D but not 3D visual naming skills. We have also pointed to the importance of using ecologically relevant tasks when comparing literate and illiterate subjects. We also demonstrate the applicability of a network approach in elucidating differences in the functional organization of the brain between groups. The strength of such an approach is the ability to study patterns of interactions between functionally specialized brain regions and the possibility to compare such patterns of brain interactions between groups or functional states. This complements the more commonly used activation approach to functional neuroimaging data, which characterize functionally specialized regions, and provides important data characterizing the functional interactions between these regions.     

A Note on (K)Nots: Response to Robert W. Kentridge''s Commentary

GY, an extensively studied human hemianope, is aware of salient visual events in his cortically blind field but does not call this "vision." To learn whether he has low-level conscious visual sensations or whether instead he has gained conscious knowledge about, or access to, visual information that does not produce a conscious phenomenal sensation, we attempted to image process a stimulus s presented to the impaired field so that when the transformed stimulus T(s) was presented to the normal hemifield it would cause a sensation similar to that caused by s in the impaired field. While degradation of contrast, spatio-temporal filtering, contrast reversal, and addition of smear and random blobs all failed to match the response to a flashed bar s(f), moving textures of low contrast were accepted to match the response to a moving contrast-defined bar, s(m). Orientation and motion direction discrimination of the perceptually matched stimuli [s(m) and T(s(m))] was closely similar. We suggest that the existence of a satisfactory match indicates that GY has phenomenal vision.     

Hemispheric asymmetry in lexical decisions: the effects of grammatical class and imageability

It has been suggested that neural systems for lexical processing of nouns and verbs are anatomically distinct. The aim of the present study was to investigate if brain asymmetry for the processing of these two grammatical classes is also different. Neurologically intact adults performed a lateralized lexical decision task with grammatically unambiguous words of high, medium, and low degrees of imagery. For error scores a right visual field (RVF) advantage and an overall effect of imageability were obtained. For latency scores grammatical class and imageability modified visual field differences: in the noun class a RVF advantage was obtained only for low imagery nouns, while for the verbs the RVF advantage was present for both medium and low imagery verbs. These results suggest that the participation of right hemisphere neural systems in the processing of verbs is more limited than in the processing of nouns.     

Recognition Memory for Faces: Reliability and Validity of the Warrington Recognition Memory Test (RMT) in a Neurological Sample

In response to critiques regarding the psychometric limitations of the Warrington Recognition Memory Test for faces (RMT-F), the current study was conducted to examine the test-retest reliability and validity of the measure in a neurological sample. Forty adult outpatients, ages 35–81, were administered the RMT-F as part of their diagnostic exam. A second evaluation was conducted after an average interval of 7 months (range = 2–20 months). Results yielded a Pearson reliability coefficient of 0.81 (p < .001), indicating a clinically satisfactory index of stability. Correlations with other measures were conducted to examine convergent and divergent validity. Results indicate that the facial component of the RMT has adequate reliability for patients with established neurological disease, shows moderate correlations with other measures of complex visuospatial function, and shows no significant correlation with measures of verbal reasoning, visual problem-solving, or verbal fluency. These findings provide additional support for the clinical efficacy of this instrument for use in a diverse neurological patient sample.     

Qualitative analyses of critical aspects of adaptation to the visually left-right reversed world

In this article, mechanisms of perceptual adaptation to the transposed world are analyzed based on introspective and behavioral performance data gathered during an extended period of wearing left-right reversing goggles. Three aspects central to this study were the mental map of the living space surrounding the subject, body image (both seen and felt), and the sensorimotor coordination system, which reflects the relationship between the subject and surroundings. These were investigated through map-drawing tests, self-representation tests when postures other than face forward were adopted, and after effects observed immediately after removal of the reversing goggles. It was concluded that the main course of the perceptual adaptation to the visually left-right reversed world consists of double reversals of the mental map and body image as well as the establishment of a new sensorimotor coordination system. In sharp contrast to the proprioceptive-change hypothesis, the importance of the visual nature of the body image was emphasized.     

远、近空间内注意加工的分离

临床证据发现空间忽视症病人对于近处和远处空间内的注意加工存在差异,表现为空间忽视只发生于近处空间或只发生于远处空间,提示近处空间与远处空间在脑内可能是分别表征的。对健康成人的研究也发现了与之类似的近处空间和远处空间注意的分离现象,即在近处空间表现出左偏的伪忽视现象,在远处空间表现出左偏减弱或者右偏的趋势。本文综述了远、近空间内注意加工分离的实验证据以及采用线段二分任务这一主要的研究范式相关的实验结果,并且着重指出了远、近空间的划分不是绝对的,而是动态可变的研究证据。最后,指出了将来的研究需要深入考察空间参照系统在远、近空间知觉中的作用,以及关注社会交互情境下的远、近空间距离认知的动态变化。