CRT screens may give rise to biased estimates of interhemispheric transmission time in the Poffenberger paradigm.

It has been shown that computer video-display units do not emit luminance uniformly over the entire screen, but emit more light on the right hand side than on the left hand side. The present study investigates whether this luminance asymmetry has implications for the manual and vocal estimates of interhemispheric transmission time (IHTT) in the Poffenberger paradigm. In particular, it is shown that previous reports of right visual-field advantages for vocal responses are an artifact of the luminance asymmetry of computer screens and that this asymmetry also has implications for estimates of differences in transmission time from the right to the left hemisphere in manual responses. In addition, we examined the impact of stimulus intensity and dark adaptation to the IHTT estimates and found that neither had an effect. This is in line with previous evidence that interhemispheric transfer in the Poffenberger paradigm does not depend on the transfer of visual information.

Bilateral field interactions and hemispheric asymmetry in number comparison.

We investigated bilateral field interactions and hemispheric asymmetry in number comparison. A numerical comparison task with three different stimulus notations (Arabic numerals, word numerals and bar graphs) was used. In all conditions, a target was displayed in one visual field, simultaneously with a distractor of the same format in the other visual field. Participants had to indicate manually whether the magnitude of the target was small or large, ignoring the distractor stimulus. Only in the condition with Arabic numerals did we obtain some evidence for a LVF advantage, which argues against a strong laterality of number magnitude representations. Significant interactions between target and distractor values were observed, indicating rich interhemispheric interactions. The interactions were mainly situated at the response stage, but the presence of a bilateral identity effect also points to interactions at the input level.

Sentence reading: do we make use of orthographic cues in homophones?

Starting from the finding that currently phonological models of visual word processing predominate, we examined what happened when important morphological information is disclosed in the orthography but not in the phonology. To do so, we made use of a peculiarity in Dutch. In this language, some forms of the present and the past tense of verbs are homophones or homographs. This allowed us to look at the power of orthographic and phonological cues to derive the tense of the verb. Two experiments showed that orthographic cues alone suffice to recover the tense of the verb, and that this recovery does not take more time than tense recovery on the basis of a combination of orthographic and phonological cues. On the basis of these results, we conclude that orthographic cues in homophones are very efficient during silent reading. Our findings, however, do not allow us to conclude whether this is due to a direct route from orthography to meaning, or to a specialised, morpho-syntactic back-up strategy elicited by certain sequences of letters.

Age and interhemispheric transfer time: a failure to replicate.

In a recent study with the Poffenberger paradigm, Brizzolara et al. reported longer estimates of interhemispheric transfer time (IHTT) for children aged 7 years than for adults. They interpreted this finding as evidence for incomplete functional maturity of the corpus callosum in young children. The present study was we were unable to replicate the age effect reported by Brizzolara et al. A closer look at the original study revealed that only 80 observations per child had been collected, which makes it probable that the larger IHTTs in 7-year-olds were caused by stimulus-response compatibility rather than by the lower efficiency of the corpus callosum during childhood years.