Blog Archives

Evidence for right hemisphere phonology in a backward masking task

The extent to which orthographic and phonological processes are available during the initial moments of word recognition within each hemisphere is under specified, particularly for the right hemisphere. Few studies have investigated whether each hemisphere uses orthography and phonology under constraints that restrict the viewing time of words and reduce overt phonological demands. The current study used backward masking in the divided visual field paradigm to explore hemisphere differences in the availability of orthographic and phonological word recognition processes. A 20 ms and 60 ms SOA were used to track the time course of how these processes develop during pre-lexical moments of word recognition. Nonword masks varied in similarity to the target words such that there were four types: orthographically and phonologically similar, orthographically but not phonologically similar, phonologically but not orthographically similar and unrelated. The results showed the left hemisphere has access to both orthography and phonology early in the word recognition process. With more time to process the stimulus, the left hemisphere is able to use phonology which benefits word recognition to a larger extent than orthography. The right hemisphere also demonstrates access to both orthography and phonology in the initial moments of word recognition, however, orthographic similarity improves word recognition to a greater extent than phonological similarity.

from Brain and Language

Attention and the identification of parafoveal words in school-age children and adults

The goal of this study was to examine whether reading parafoveal words is more attention-demanding in 7- to 10-year-old children (2nd to 5th grade) than in adults, and whether this increase in attention interacts with visual field. In an identification task, we presented 4-letter words in the left (LVF) or right (RVF) visual fields in single unilateral (one word in one visual field), unilateral with distractor (one word + one distractor in the opposite visual field) and bilateral (two words) conditions. We also presented object drawings. The results showed that all groups of children were more sensitive to the presence of a second stimulus (distractor or word) than adults in the block of words, but not in the block of object drawings. We interpreted this result as indicating an age-related change in the attentional demands of word identification and in attentional control when reading, thus in the interaction between the attentional control system and the language network. As well, we found the same RVF superiority for words and the same attentional bias (larger distractor effect on LVF words) in children and adults, which is not in favor of the hypothesis of an age-related change in language lateralization.

from the Journal of Neurolinguistics

Left visual-field advantage in the dual-stream RSVP task and reading-direction: A study in three nations

In the dual-stream Rapid Serial Visual Presentation task, a stream of stimuli containing two target stimuli is rapidly presented left and right. In previous studies, the second target was better identified in the left than in the right-hemifield. In all those studies, alphanumeric stimuli were used both as targets and distracters. We examined to what extent this left visual-field advantage is dependent on reading-direction. The task was performed by Germans (with Latin characters), Israelis (with Latin and Hebrew characters) and Taiwanese (with Latin and Chinese characters). If caused by overlearnt associative links between Latin characters and left-to-right reading, the prominent left visual-field bias should be reversed in Hebrew and disappear in Chinese. Furthermore, if caused by direction of reading in the participant’s native language, the left visual-field advantage in Latin conditions should be larger in Germans than in Israelis and Taiwanese. A left visual-field advantage was always observed, though slightly smaller in Hebrew and in Chinese, and there was no difference in the Latin conditions between the three nations. Therefore, it seems that the left visual-field advantage in speeded target identification is not primarily caused by the left-to-right reading-direction, but may be a combined effect resulting from the asymmetric organization of general mechanisms of visual processing and from stimulus-induced preferences.

from Neuropsychologia

Hemispheric involvement in reading: The effects of language experience

The goal of this study was to examine whether readers of Hebrew generalize their native-language processing strategies to the representation of English words. To this end, we examined lateralization patterns in the lexical decisions of native English and Hebrew readers to English stimuli, and compared the performance of native Hebrew speakers in English and in Hebrew. We used both unilateral and bilateral presentation modes, which allowed us to assess interhemispheric communications, and manipulated the morphological complexity of the stimuli. The results showed the following pattern: English speakers showed an RVFA for words and not for nonwords, with interhemispheric patterns suggesting independent LH processing and dependent RH processing of words. Hebrew speakers showed no visual field advantage in English, whereas they show an RVFA when they read Hebrew. Findings suggest that the division of labor between the two hemispheres is determined by linguistic experience, whereas the effects of morphological manipulations reflect the structure of the language of the test.

from the Journal of Neurolinguistics

The left visual-field advantage in rapid visual presentation is amplified rather than reduced by posterior-parietal rTMS

In the present task, series of visual stimuli are rapidly presented left and right, containing two target stimuli, T1 and T2. In previous studies, T2 was better identified in the left than in the right visual field. This advantage of the left visual field might reflect dominance exerted by the right over the left hemisphere. If so, then repetitive transcranial magnetic stimulation (rTMS) to the right parietal cortex might release the left hemisphere from right-hemispheric control, thereby improving T2 identification in the right visual field. Alternatively or additionally, the asymmetry in T2 identification might reflect capacity limitations of the left hemisphere, which might be aggravated by rTMS to the left parietal cortex. Therefore, rTMS pulses were applied during each trial, beginning simultaneously with T1 presentation. rTMS was directed either to P4 or to P3 (right or left parietal cortex) either as effective or as sham stimulation. In two experiments, either one of these two factors, hemisphere and effectiveness of rTMS, was varied within or between participants. Again, T2 was much better identified in the left than in the right visual field. This advantage of the left visual field was indeed modified by rTMS, being further increased by rTMS to the left hemisphere rather than being reduced by rTMS to the right. It may be concluded that superiority of the right hemisphere in this task implies that this hemisphere is less irritable by external interference than the left hemisphere.

from Experimental Brain Research

Split fovea theory and the role of the two cerebral hemispheres in reading: a review of the evidence

Split fovea theory proposes that when the eyes are fixated within a written word, visual information about the letters falling to the left of fixation is projected initially to the right cerebral hemisphere while visual information about the letters falling to the right of fixation is projected to the left cerebral hemisphere. The two parts of the word must be re-united before the word can be recognised. Bilateral projection theory proposes instead that visual information is projected simultaneously to both hemispheres provided that it falls within the fovea (defined as the central 2 to 3 degrees). On this more traditional account, no interhemispheric transfer would be required in order to read a word presented within the fovea. We review the evidence in support of split fovea theory and consider some of the objections that have been raised. We argue that a split fovea affects the reading of words at fixation, something that must be recognised and accounted for by cognitive, computational and neural models of reading.

from Neuropsychologia

The sensitivity of the right hemisphere to contextual information in sentences

One explanation for the inconsistencies in research examining the sentence comprehension abilities of the right hemisphere (RH) is the presence of confounding variables that have generally served to disadvantage the processing capacities of the RH. As such, the present study aimed to investigate hemispheric differences in the use of message-level sentential information by removing some of the factors known to be inherently disadvantageous for RH comprehension. Thirty-two right-handed undergraduate university students participated in a computer-based lexical decision task where RT and error rates were recorded. The sensitivity of each hemisphere to the message-level contextual information contained in short versus long sentences was compared, as well as the effect of stimulus modality (visual compared to auditory). The results showed that the RH benefited from increased levels of context to at least the same extent as the LH and that, more importantly, this could not be explained by word-level processes alone. This finding, unusual in behavioral research on normal individuals but consistent with neuropsychological, electrophysiological, and neuroimaging approaches, suggests that the RH plays an important role in sentence comprehension, at least in relation to sentences that conform to a relatively simple structure.

from Brain and Language