Left Visual Field Right Hemisphere Research Articles

Visual interalisation effect in reading Chinese characters.

Visual half-field experiments have been used to investigate perceptual differences in reading different types of writing scripts. It has been observed that tachistoscopic recognition of phonetic-based scripts (such as the English alphabet and Japanese Kana) tends to show a right visual field–left hemisphere (RVF-LH) superiority effect1,2 whereas recognition of logographic symbols (for example, Chinese characters) tends to show a left visual field–right hemisphere (LVF-RH) superiority effect3,4. A cerebral orthography-specific localisation hypothesis has been proposed to account for these data. We have conducted three experiments to examine the visual lateralisation effect in reading logographic symbols such as Chinese characters. Chinese subjects in the first experiment were exposed to brief tachistoscopic presentation of a single character, and their task was to name the character as soon as possible. A LVF-RH superiority was found. In the second experiment, the stimuli were two vertically arranged characters and the subjects were asked to name the stimulus terms as soon as possible. The third experiment was the same as the second except that the task was to decide whether these character-strings were correct semantic terms with a manual response. A RVF-LH superiority effect was found in both the second and third experiments. These differential visual lateralisation results were interpreted as reflecting the function-specific property of the two hemispheres and cast doubt on the orthography-specific localisation hypothesis proposed by earlier investigators.

Information processing in the cerebral hemispheres: selective hemispheric activation and capacity limitations.

Several previous experiments have found that concurrently maintaining verbal information in memory influences visual laterality patterns (e.g., Hellige & Cox, 1976; Kinsbourne, 1975). The present article critically reviews existing experiments and reports five additional experiments designed to identify the mechanisms responsible for such effects. Experiment 1 demonstrates that laterality patterns are not influenced by a concurrent memory task that does not require verbal processing. (The verbal nature of the concurrent task was an important aspect of previous experiments.) Experiments 2 and 3 were designed to determined whether concurrent verbal memory primarily influences very early visuospatial processes or later processes such as those involved in visuospatial memory. In Experiment 2, observers indicated whether two simulteneously presented nonsense forms had the same shape. Observers held 0, 2, 4, or 6 words in memory during each shape judgment trial. Responses were faster when the forms were presented to the left visual field--right hemisphere (LVF-RH) than to the right visual field--left hemisphere (RVF-LH). This effect did not interact with memory set size. In Experiment 3, observers indicated whether either of two simultaneously presented forms was identical to a target form held in memory. Observers held 0, 2, or 6 words in memory on each trial. On same-as-target trials, responses were faster on LVF-RH trials than on RVF-LH trials in the no-word memory condition; this difference was reversed in the two-word and six-word conditions. The combined results of Experiments 2 and 3 suggest that concurrent verbal memory influences stages of processing beyond the initial registration of visuospatial information. Experiments 4 and 5 examined the influence of concurrent verbal memory on verbal laterality tasks. Observers indicated whether two simultaneously presented letters of different cases had the same name. In Experiment 4, different groups of observers held 0, 2, 4, or 6 words in memory on each letter-pair trial. In Experiment 5, memory set size was manipulated within subjects. On the same-pair trials of Experiment 4 and the first session of Experiment 5, responses in the no-memory condition were faster on RVF-LH trials than on LVF-RH trials; this difference was reversed in all of the work memory conditions. This shift is opposite to that found when the laterality task does not require verbal processing and further indicates that concurrent verbal memory influences processing stages beyond those that are common to the form-pair and letter-pair tasks. Neither directness-of-pathway nor attention-gradient laterality models can explain the entire pattern of results from the present experiments. Rather, the results suggest that the left hemisphere functions as a typical limited-capacity information processing system that can be influenced somewhat separately from the right hemisphere system.