Journal of Psycholinguistic Research, VoL 22, No. 5, 1993 Are Morphological Structures Computed During Word Recognition? Gary Libben x In the recent literature in generative morphology, it has been assumed that multimor- phemic words must be characterized as having a hierarchical internal structure which is expressible in the form of morphological trees. This paper reports on an experiment which addresses the following question: Are these structures relevant to complex word recognition? In a naming latency experiment, subjects were presented with prefixed and suffi~d nonsense roots. The use of stimuli such as these allowed for the control of real word effects such as frequency and semantic plausibility and made it possible to system- atically vary the configuration of the morphological trees. Significant response time differences were found between the morphologically illegal forms and legal configura- tions. This was taken as evidence that subjects do compute morphological representa- tions. Because no differences were found between legal left-branching structures and legal right-branching structures, it was concluded that morphological computation is not sensitive to the serial ordering of morphemes within a complex word. Anyone who has taught introductory courses in English morphology has had to come to grips with the initial reactions of native speaker students to linguists" representations of complex word structure. The notion that compounds such as blackboard and inflected forms such as watching are composed of two morphemes that must be arranged in the manner dis- played in Fig. 1 is relatively acceptable. However, the representation of complex derived forms such as unforeseeability and reintroduction in Fig. 2 typically strike native speakers as unduly elaborate. This research was supported by Social Sciences and Humanities Council of Canada research grant 410-90-1502 to the author. 1 Address all correspondence to Gary Libben, Department of Linguistics, 4-36A Assi- niboia Hall, University of Alberta, Edmonton, Alberta, Canada T6G 2E7. 535 0090-6905/93/0900-0535507.00/0 9 1993 Plenum Publishing Corporation