Biomedical subjects

Karen Banai

Publications and source records attributed to Karen Banai.

6 recordsLinked to original sources

PubMed2006

Dyslexia and the failure to form a perceptual anchor.

In a large subgroup of dyslexic individuals (D-LDs), reading difficulties are part of a broader learning and language disability. Recent studies indicate that D-LDs perform poorly in many psychoacoustic tasks compared with individuals with normal reading ability. We found that D-LDs perform as well as normal readers in speech perception in noise and in a difficult tone comparison task. However, their performance did not improve when these same tasks were performed with a smaller stimulus set. In contrast to normal readers, they did not benefit from stimulus-specific repetitions, suggesting that they have difficulties forming perceptual anchors. These findings are inconsistent with previously suggested static models of dyslexia. Instead, we propose that D-LDs' core deficit is a general difficulty in dynamically constructing stimulus-specific predictions, deriving from deficient stimulus-specific adaptation mechanisms. This hypothesis provides a direct link between D-LDs' high-level difficulties and mechanisms at the level of specific neuronal circuits.

Adaptation, Psychological↗

PubMed2006

Auditory processing deficits in dyslexia: task or stimulus related?

The nature of the fundamental deficit underlying reading disability is the subject of a long-standing debate. We previously found that dyslexics with additional learning difficulties (D-LDs) perform poorly in simple auditory tasks. We now tried to determine whether these deficits relate to stimulus or task complexity. We found that the degree of impairment was dependent on task rather than stimulus complexity. D-LDs could adequately detect and identify mild frequency changes in simple pure tones and minimal phonemic changes in complex speech sounds when task required only simple same-different discriminations. However, when task required the identification of the direction of frequency change or the ordinal position of a repeated tonal or speech stimulus, D-LDs' performance substantially deteriorated. This behavioral pattern suggests that D-LDs suffer from a similar type of deficits when processing speech and nonspeech sounds. In both cases, the extent of difficulties is determined by the structure of the task rather than by stimulus composition or complexity.

Acoustic Stimulation↗

PubMed2005

Brainstem timing: implications for cortical processing and literacy.

The search for a unique biological marker of language-based learning disabilities has so far yielded inconclusive findings. Previous studies have shown a plethora of auditory processing deficits in learning disabilities at both the perceptual and physiological levels. In this study, we investigated the association among brainstem timing, cortical processing of stimulus differences, and literacy skills. To that end, brainstem timing and cortical sensitivity to acoustic change [mismatch negativity (MMN)] were measured in a group of children with learning disabilities and normal-learning children. The learning-disabled (LD) group was further divided into two subgroups with normal and abnormal brainstem timing. MMNs, literacy, and cognitive abilities were compared among the three groups. LD individuals with abnormal brainstem timing were more likely to show reduced processing of acoustic change at the cortical level compared with both normal-learning individuals and LD individuals with normal brainstem timing. This group was also characterized by a more severe form of learning disability manifested by poorer reading, listening comprehension, and general cognitive ability. We conclude that abnormal brainstem timing in learning disabilities is related to higher incidence of reduced cortical sensitivity to acoustic change and to deficient literacy skills. These findings suggest that abnormal brainstem timing may serve as a reliable marker of a subgroup of individuals with learning disabilities. They also suggest that faulty mechanisms of neural timing at the brainstem may be the biological basis of malfunction in this group.

Acoustic Stimulation↗

PubMed2004

Poor frequency discrimination probes dyslexics with particularly impaired working memory.

Substantial difficulties in performing simple auditory discriminations were previously found in some individuals with a specific reading disability but not in others. This high variability in psychoacoustic performance raises the question of whether this difficulty is related to the reading deficit. Addressing this question, we compared adult dyslexics with and without difficulty in simple auditory discriminations, using 2-tone frequency discrimination as our probe. The distribution of their frequency discrimination scores was bimodal. On this basis, we divided our participants into subgroups having either poor or adequate psychoacoustic performance. Only dyslexics with poor psychoacoustic scores had significantly impaired verbal working memory compared to their matched controls. Furthermore, and only in this subgroup, working memory scores were correlated with both cognitive abilities and reading-related tasks. Consistent with the hypothesis that in this subgroup poor working memory impedes performance in a broad range of academically related tasks, we found that the majority of dyslexics in this subgroup had more extensive academic difficulties and consequently needed special support in schools. We propose that dyslexics with poor psychoacoustic abilities form a distinct subtype of dyslexia in which the core deficit is not specific to phonological components. For these individuals, poor verbal working memory may be the main impediment to success in academic environments.

Adolescent↗

PubMed2004

Patterns of deficit in auditory temporal processing among dyslexic adults.

We characterized temporal psychoacoustic performance in a group of adult dyslexics with excellent cognitive abilities. These individuals performed adequately on a two-tone frequency discrimination task when inter-stimulus intervals were long ( > or =1 s or more). However, their performance gradually deteriorated as interval duration was shortened (0.7- 0.1 s). Dyslexics with similar reading abilities, but with average cognitive abilities, performed poorly at all intervals. These findings show that, though both groups suffer from non-phonological deficits in auditory discrimination, the nature of their deficits differs. Dyslexics with excellent cognitive abilities seem to have slow, yet adequate, stimulus identification and comparison mechanisms. The fundamental impairment of the other dyslexic group is difficult to determine because their performance was poor across all intervals.

Acoustic Stimulation↗

PubMed2002

Disabled readers suffer from visual and auditory impairments but not from a specific magnocellular deficit.

The magnocellular theory is a prominent, albeit controversial view asserting that many reading disabled (RD) individuals suffer from a specific impairment within the visual magnocellular pathway. In order to assess the validity of this theory we tested its two basic predictions. The first is that a subpopulation of RD subjects will show impaired performance across a broad range of psychophysical tasks relying on magnocellular functions. The second is that this subpopulation will not be consistently impaired across tasks that do not rely on magnocellular functions. We defined a behavioural criterion for magnocellular function, which incorporates performance in flicker detection, detection of drifting gratings (at low spatial frequencies), speed discrimination and detection of coherent dot motion. We found that some RD subjects (six out of 30) had impaired magnocellular function. Nevertheless, these RD subjects were also consistently impaired on a broad range of other perceptual tasks. The performance of the other subgroup of RD subjects on magnocellular tasks did not differ from that of controls. However, they did show impaired performance in both visual and auditory non-magnocellular tasks requiring fine frequency discriminations. The stimuli used in these tasks were neither modulated in time nor briefly presented. We conclude that some RD subjects have generally impaired perceptual skills. Many RD subjects have more specific perceptual deficits; however, the "magnocellular" level of description did not capture the nature of the perceptual difficulties in any of the RD individuals assessed by us.

Adolescent↗