Behavioral estimates of interhemispheric transmission time and the signal detection method: A reappraisal

Abstract

On the basis of a review of the literature, Bashore (1981) concluded that only simple reaction time experiments with manual responses yielded consistent behavioral estimates of interhemispheric transmission time. A closer look at the data, however, revealed that these experiments were the only ones in which large numbers of observations were invariably obtained from many subjects. To investigate whether the methodological flaw was the origin of Bashore's conclusion, two experiments were run in which subjects had to react to lateralized light flashes. The first experiment dealt with manual reactions, the second with verbal reactions. Each experiment included a condition without catch trials (i.e., simple reaction time) and two conditions with catch trials. Catch trials were trials in which no stimulus was given and in which the response was to be withheld. Both experiments returned consistent estimates of interhemispheric transmission time in the range of 2-3 msec. No differences were found between the simple reaction time condition and the signal detection conditions with catch trials. Data were analyzed according to the variable criterion theory. This showed that the effect of catch trials, as well as the effect of interhemispheric transmission, was situated at the height of the detection criterion, and not in the rate of the information transmission.

Interhemispheric transfer of colour and shape information in the presence and absence of the corpus callosum

“…The median RT increased with increasing task complexity, but the mean CUD decreased, if anything, and was virtually zero (and actually slightly negative) for the two-choice and threechoice tasks. The mean CUD of 6 ms for the go±no go task is in marked contrast to the prolonged CUD for simple detection tasks reported in the studies reviewed by Bashore [4], but is consistent with the more recent results of Brysbaert [9]. The absence of any RT advantage under the crossed conditions in the two-choice and three-choice tasks supports Po enberger's [39] suggestion that the use of the CUD as a measure of IHTT applies only to simple RT tasks, and may not be valid for the e ects found in these more complex tasks.…”

“…A review of ®ve experiments on simple detection suggested that this slight increase in task complexity creates longer RTs and greater variability in CUD, which ranged from 5 to 28.5 ms in the reviewed studies [4,8]. In a more recent study, however, Brysbaert [9] found a constant CUD of 2.4 ms in simple detection experiments with varying numbers of catch trials.…”

Age and interhemispheric transfer time: a failure to replicate

“…They attributed this increase to incomplete maturity of the corpus callosum at the age of 7 years. In the present experiment we investigated whether the higher IHTT-measure for young children also implied that their IHTT estimate is a function of stimulus intensity, as previously demonstrated in split-brain patients and acallosals [11,17], and predicted by the variable-criterion model of Brysbaert [9].…”

“…What is often overlooked, however, is that the findings of Berlucchi et al were based on a total of more than 1000 trials per subject and with adults. Brysbaert [9] presented evidence that when the number of trials is smaller and the subjects less experienced, stimulus-response compatibility is likely to confound the CUD estimates. In their study, Brizzolara et al only had 80 observations per child and they did not make reference to any practice trials.…”

“…They have a larger CUD for faint light flashes than for bright light flashes [11]. This property is not shared by normal individuals whose CUD remains stable over a wide range of intensities [9,11]. We hypothesized that if the 21 ms CUD of 7-year old children has the same origin as the 18 ms CUD of acallosals, then it should similarly be affected by the brightness of the light flash.…”