Differential gamma-band responses to word and pseudoword presentation cannot be an artifact of power changes in lower frequency bands because analysis of low frequency bands did not reveal such changes. Linguistic units, such as phonemes and morphemes, are well-defined entities. Thus, there is no motivation for the criticisms raised in Mueller & Jokeit's commentary.
2. We wish to remind Mueller & Jokeit of paragraphs 20 and 23 of our target article, where we report that word/pseudoword differences were observed in the gamma range, but not in other frequency bands. This was demonstrated in two different experiments. The commentator' speculation that there may be a difference in spectral responses in lower frequencies is, therefore, not motivated. To make this even more evident, we report here an analysis of spectral responses of the 10-20 Hz band from our EEG experiment. The analysis procedure was exactly the same as for the 25-35 Hz band, where a significant interaction of the factors Wordness and Hemisphere was obtained with reduced power over the left hemisphere after pseudowords. (The procedure is detailed in Lutzenberger et al., 1994.) In the 10-20 Hz band (that is, in the high alpha plus beta band), there was no significant main effect of the factor Wordness nor a significant interaction of this factor with other variables. In the time window 320-520 ms post stimulus onset, where the analysis of the 25-35 Hz band revealed significant word/pseudoword differences over the left hemisphere, the 10-20 Hz band revealed a Wordness x Hemisphere interaction being far from significant (F (1,14) = 1.2, p = 0.29, n.s.). There was not even a tendency towards a power difference between 10-20 Hz responses to words and pseudowords. Dynamics of gamma-band power cannot, therefore, be due to power changes in lower frequency bands.
3. Of course, Mueller & Jokeit are right regarding what they say about event-related desynchronization (ERD). They may well re-label what we describe as gamma depression as gamma-range ERD, as long as they add that ERD is usually seen only in the alpha (and sometimes beta) band. However, this re-labelling does not explain which neurophysiological processes underlie these EEG and MEG phenomena. We believe that this is an important issue which can be addressed on the basis of our data. If Mueller & Jokeit do not believe in our model, they are very welcome to come up with an alternative explanation. Tagging a phenomenon "ERD" is not an explanation.
4. If Mueller & Jokeit believe that "in linguistics, there is no consensus about the basic units of language comprehension" (par. 2), they are certainly mistaken. Among the few things that all linguists agree upon, is the distinction between phonemes (elements that DISTINGUISH meaning) and morphemes (elements that CARRY meaning). These elements are not "artificial", as Mueller & Jokeit believe, but are very real. The fact that speech-analysis computers have great difficulty locating word boundaries in connected speech is an entirely different issue. In our experiments, words (most of which included only one morpheme) were presented one by one, so that the segmentation problem was solved by the interstimulus interval. Most important, linguistic units are not only well-defined, but, in addition, are very useful as stimulus material in experiments in psychophysiology and cognitive neuroscience. Distinguishing a meaningful word from a meaningless pseudoword is quite easy, while distinguishing diagrams that represent "Gestalts" from those that don't appears to be much more difficult. The result is that if language material is used in a psychophysiological experiment, clear predictions on the presence and activation of cortical representations can be stated. However,this may be more difficult for nonlinguistic visual material.
5. "There is no evidence for the tantalizing statement that the hierarchy of linguistic structures has its biological equivalent in a hierarchy of cell assemblies corresponding to these cognitive entities" (Mueller & Jokeit, 1994). It depends on what one means by "evidence". It has certainly not been demosntrated. However, there are data that can easily be accounted for by the cell assembly model, while competing models have great difficulty explaining them (Braitenberg & Pulvermueller, 1992; Mohr et al., 1994a; 1994b). It seems unwise to dismiss a potentially fruitful approach to the theory of cognitive brain processes.
Braitenberg, V. & Pulvermueller, F. (1992) Entwurf einer neurologischen Theorie der Sprache. Naturwissenschaften 79:103-117.
Lutzenberger, W., Pulvermueller, F. & Birbaumer, N. (1994) Words and pseudowords elicit distinct patterns of 30-Hz activity in humans. Neuroscience Letters 176:115-118.
Mohr, B., Pulvermueller, F., Rayman, J. & Zaidel, E. (1994a) Interhemispheric cooperation during lexical processing is mediated by the corpus callosum: evidence from the split-brain. Neuroscience Letters 181:17-21.
Mohr, B., Pulvermueller, F. & Zaidel, E. (1994b) Lexical decision after left, right and bilateral presentation of content words, function words and non-words: evidence for interhemispheric interaction. Neuropsychologia 32:105-124.
Mueller, H.M. & Jokeit, H. (1994) Word Processing and Gamma Band Activity. Commentary on Pulvermueller et al., on Brain-Rhythms. PSYCOLOQUY 5(60) brain-rhythms.5.mueller.
Pulvermueller, F., Preissl, H., Eulitz, C., Pantev, C., Lutzenberger, W., Elbert, T. & Birbaumer, N. (1994) Brain Rhythms, Cell Assemblies and Cognition: Evidence from the Processing of Words and Pseudowords. PSYCOLOQUY 5(48) brain-rhythms.1.pulvermueller.