Cortical locus of coherent motion deficits in deaf poor readers

Samar and Parasnis [Samar, V. J., & Parasnis, I. (2005). Dorsal stream deficits suggest hidden dyslexia among deaf poor readers: correlated evidence from reduced perceptual speed and elevated coherent motion detection thresholds. Brain and Cognition, 58, 300-311.] reported that correlated measures of coherent motion detection and perceptual speed predicted reading comprehension in deaf young adults. Because deficits in coherent motion detection have been associated with dyslexia in the hearing population, and because coherent motion detection is strongly dependent on extrastriate cortical area MT, these results are consistent with the claim that hidden dyslexia occurs within the deaf population and is associated with deficits in MT. However, coherent motion detection can also be influenced by subcortical deficits in both magnocellular and parvocellular pathways. To confirm the putative cortical locus of coherent motion perception deficits, we measured contrast thresholds for detecting the direction of movement of drifting sine wave gratings in the same participant group as [Samar, V. J., & Parasnis, I. (2005). Dorsal stream deficits suggest hidden dyslexia among deaf poor readers: correlated evidence from reduced perceptual speed and elevated coherent motion detection thresholds. Brain and Cognition, 58, 300-311.], under stimulus conditions that selectively biased for input from the subcortical magnocellular and parvocellular pathways, respectively. Contrast thresholds were not related to reading comprehension performance under either the magnocellular or parvocellular conditions. Furthermore, the previously reported correlations among reading comprehension, coherent motion thresholds, and perceptual speed remained significant even after contrast thresholds and non-verbal IQ were controlled in partial correlation analyses. In addition, coherent motion detection thresholds were found to correlate specifically with a reading-IQ discrepancy score, one commonly used indicator of dyslexia. These results provide direct psychophysical evidence that the previously reported deficit in coherent motion detection in deaf poor readers does not involve subcortical pathway deficits, but rather is associated with a cortical deficit likely involving area MT. They also strengthen the argument for the existence of hidden dyslexia in the deaf adult population.     

An electrophysiological model of working memory performance

Working memory (WM) enables us to keep a limited amount of information in active mode. It is believed that attention refreshes necessary information in WM and prevents their forgetting. Despite a plethora of models offered, it is not fully understood that what factors may be involved in forgetfulness and in the required time for refreshing the information. In this study, an electrophysiological model of WM is proposed that consists of several resistor-capacitor units. Inspired of the “resource capacity theory,” attention as a limited source of energy refreshes the voltage level of these units. According to the “time-based resource sharing theory,” only one of these units is allowed to use the limited source of attention at each moment. The source of attention is shared between active units. This model mimics the pattern of several well-known observations of WM such as the recall interval, the word length, and the serial position effect. Some suggestions have been provided about influencing factors in WM performance. Model parameters give the ability of investigating the possible effect of some other factors on WM performance and also a probable prediction about how much information can we chunk?