The goal of this dissertation was to test the hypothesis that great apes can solve both visible and invisible displacements, whereas monkeys can solve only visible displacements. First, rhesus monkeys, squirrel monkeys, and orangutans received visible and invisible displacement tests that correspond to Stages 4, 5, and 6 of object permanence. Monkeys and orangutans were successful on the visible displacement tests. Most orangutans were successful on all invisible displacement tests except the double displacements. The monkeys were not successful on invisible displacement tests and they had a location preference. Subsequent testing revealed that (1) rhesus monkeys eventually solved single and control invisible displacements, (2) two rhesus monkeys eventually solved double displacements, (3) using a familiar containment device improved performance on invisible displacements and (4) most orangutans eventually solved double invisible displacements when the object was concealed in a cup. In the second part of the dissertation, I determined if poorer performance on invisible displacements was related to increased memory requirement. The primates received three types of problems that had equivalent memory requirement. On Invisible transfer problems, the object was hidden in a box and then invisibly transferred to another box, whereas on Visible transfer problems the object was visibly transferred, and on No transfer problems, it was not transferred. The rhesus monkeys and the squirrel monkeys solved the Visible and the No transfer problems. Only one monkey was successful on the Invisible transfer problems. Given that all problems had equivalent memory requirements, this variable cannot account for poorer performance on Invisible transfer problems. Most orangutans solved all three types of problems. Nevertheless, the performance of the orangutans on Invisible transfer problems was poorer than that on the other problems. Next, cueing sessions were instituted during which a clear box was used in order to allow the primates to see if and how the object was transferred. Then, the primates were re-tested on the three problems. Cuing helped monkeys and orangutans find the object on Invisible transfer problems. In summary, the results of this dissertation indicated that overall, the orangutans outperformed the monkeys on invisible displacements. However, a few orangutans performed as poorly as the monkeys on invisible displacements, and a few monkeys performed as well as the orangutans. Thus, individual differences must be taken into account to adequately portray the distribution of object permanence skills in non-human primates.

Three experiments investigated whether morphological constituents influence word processing during reading. Individuals read sentences containing free stem, bound stem, and pseudo-prefixed words. In Experiments 1 and 2, a parafoveal display change manipulation indicated that the morphological constituents of a prefixed word are not available for preprocessing in the parafovea as reading times on the target word did not differ for prefixed versus pseudo-prefixed words. Interestingly, parafoveal preview of word initial and word final letters resulted in an equivalent amount orthographic facilitation for all word types. In Experiment 3, a fast priming manipulation indicated that morphological priming effects for prefixed words are obscured during sentence processing. However, the form of the prime did facilitate subsequent word processing for all three word types. The results suggest that English prefixed words are accessed via their whole word form, as there was no evidence of morphological decomposition for prefixed words during sentence processing.

This dissertation investigates the ways in which speech perception is guided by the expectation that the stimulus is an utterance in the perceiver's language, with a particular focus on how phonotactics affects the interpretation of acoustically ambiguous segments. A model is proposed in which phonological grammar, expressed here as a system of ranked and violable constraints within the framework of phonological Optimality Theory, is used to select among competing candidate parses of the acoustic input. This grammar-based theory is contrasted with two grammarless alternative accounts of perception: the connectionist network TRACE, which derives phonotactic perceptual effects from the lexicon, and a statistical theory based on transitional probabilities. Experimental evidence is presented to show (1) that English listeners' judgments of vowels and of consonant clusters disfavor configurations which are grammatically illegal in the language, (2) that the dispreference for illegal configurations is far stronger than that for configurations which are legal but have zero frequency, and (3) that it is due to a response dependency, rather than to auditory or other stimulus factors, and cannot be explained by foreign-language exposure. Two experiments with Japanese listeners find that (1) the lexical stratum membership of nonsense words can produce a phonotactic perceptual effect, (2) that the triggering and target segments can be up to three segments distant, and (3) that the stratum-phonotactic effect is larger than a word-superiority effect obtained with the same listeners and paradigm. These results are shown to be consistent with the grammar-based model, but inconsistent with the two grammarless alternatives. Analysis of the three models reveals that the shortcomings of the alternatives is due to their inability to abstract over phoneme classes and larger linguistic structures. It is concluded that the mechanisms of speech perception have access to a full-fledged phonological competence.