Biomedical subjects

Irene P Kan

Publications and source records attributed to Irene P Kan.

6 recordsLinked to original sources

PubMed2006

Letter selection and letter assembly in acquired dysgraphia.

OBJECTIVE: We explored the constituents of the graphemic buffer in a patient with acquired dysgraphia and tested the hypothesis that the graphemic buffer is composed of 2 dissociable components: letter selection and letter assembly. BACKGROUND: Research on dysgraphia has established the graphemic buffer as a component of the spelling mechanism, and the buffer is considered a short-term memory store that is critical for letter production. However, little is known about the components within the buffer. METHOD: We devised 2 spelling tasks that rely differentially on letter selection and letter assembly. In the selection task, our patient produced the letters that composed a target word, but she did not have to provide serial position information. In the assembly task, B.H. was given all the letters of a target word and was asked to spell the word by arranging the letters in the proper serial order. RESULTS: Compared to spelling to dictation, our patient did not benefit from being given letter identity information (ie, assembly task), but her performance improved significantly when position information was available (ie, selection task). CONCLUSIONS: Based on these data, and the comparison of her performance with another dysgraphic patient, we propose that the graphemic buffer engages in both letter selection and letter assembly.

Aged↗

PubMed2006

Fractionating the left frontal response to tools: dissociable effects of motor experience and lexical competition.

A number of theories about the evolution of language posit a close (and perhaps causal) relationship between tool use and speech. Consistent with this idea, neuroimaging studies have found that tool knowledge retrieval activates not only a region of the left premotor cortex involved in hand action, but also an adjacent region that is typically described as a language center. We examined whether this pattern of activation is best described as the result of a single process, related to both action and language, or the result of two independent processes. We identified two distinct neural components that jointly contribute to this response: a posterior region centered in the premotor cortex, which responds to motor knowledge retrieval, and an anterior region centered in the left frontal operculum, which responds to lexical competition. Crucial to the interpretation of the premotor response, individual variation in motor experience was highly correlated with the magnitude of the response in the premotor cortex, but not in the prefrontal cortex.

Adolescent↗

PubMed2005

Conceptual representations of action in the lateral temporal cortex.

Retrieval of conceptual information from action pictures causes greater activation than from object pictures bilaterally in human motion areas (MT/MST) and nearby temporal regions. By contrast, retrieval of conceptual information from action words causes greater activation in left middle and superior temporal gyri, anterior and dorsal to the MT/MST. We performed two fMRI experiments to replicate and extend these findings regarding action words. In the first experiment, subjects performed conceptual judgments of action and object words under conditions that stressed visual semantic information. Under these conditions, action words again activated posterior temporal regions close to, but not identical with, the MT/MST. In the second experiment, we included conceptual judgments of manipulable object words in addition to judgments of action and animal words. Both action and manipulable object judgments caused greater activity than animal judgments in the posterior middle temporal gyrus. Both of these experiments support the hypothesis that middle temporal gyrus activation is related to accessing conceptual information about motion attributes, rather than alternative accounts on the basis of lexical or grammatical factors. Furthermore, these experiments provide additional support for the notion of a concrete to abstract gradient of motion representations with the lateral occipito-temporal cortex, extending anterior and dorsal from the MT/MST towards the peri-sylvian cortex.

Adult↗

PubMed2004

Effect of name agreement on prefrontal activity during overt and covert picture naming.

In recent neuroimaging studies, various tasks have been used to examine prefrontal cortex involvement in semantic retrieval and selection. One such task, picture naming, has yielded inconsistent results across studies. One potential explanation for this inconsistency is that the magnitude of prefrontal activity during picture naming depends on the extent to which a given picture evokes a single reliable meaning. To test this hypothesis, fMRI activity in the prefrontal cortex was measured while subjects named pictures with either high or low name agreement. In Experiment 1, subjects named black-and-white line drawings, either covertly or overtly. Across both modalities, we found more left inferior frontal gyrus (LIFG) activity when the subjects named low-agreement pictures than when they named high-agreement pictures. No significant difference in head movement was detected between the two modalities. In Experiment 2, we replicated the effect of name agreement on LIFG activity during picture naming, using black-and-white photographs. These results provide further support for the idea that the LIFG mediates selection among competing alternatives and suggest a means for understanding the naming deficits observed in nonfluent aphasia.

Adolescent↗

PubMed2004

Selection from perceptual and conceptual representations.

The lateral prefrontal cortex has been implicated in a wide variety of functions that guide our behavior, and one such candidate function is selection. Selection mechanisms have been described in several domains spanning different stages of processing, from visual attention to response execution. Here, we consider two such mechanisms: selecting relevant information from the perceptual world (e.g., visual selective attention) and selecting relevant information from conceptual representations (e.g., selecting a specific attribute about an object from long-term memory). Although the mechanisms involved in visual selective attention have been well characterized, much less is known about the latter case of selection. In this article, we review the relevant literature from the attention domain as a springboard to understanding the mechanisms involved in conceptual selection.

Attention↗

PubMed2002

Effects of frontal lobe damage on interference effects in working memory.

Working memory is hypothesized to comprise a collection of distinct components or processes, each of which may have a unique neural substrate. Recent neuroimaging studies have isolated a region of the left inferior frontal gyrus that appears to be related specifically to one such component: resolving interference from previous items in working memory. In the present study, we examined working memory in patients with unilateral frontal lobe lesions by using a modified version of an item recognition task in which interference from previous trials was manipulated. In particular, we focused on patient R.C., whose lesion uniquely impinged on the region identified in the neuroimaging studies of interference effects. We measured baseline working memory performance and interference effects in R.C. and other frontal patients and in age-matched control subjects and young control subjects. Comparisons of each of these groups supported the following conclusions. Normal aging is associated with changes to both working memory and interference effects. Patients with frontal damage exhibited further declines in working memory but normal interference effects, with the exception of R.C., who exhibited a pronounced interference effect on both response time and accuracy. We propose that the left inferior frontal gyrus subserves a general, nonmnemonic function of selecting relevant information in the face of competing alternatives and that this function may be required by some working memory tasks.

Functional Laterality↗