Infants' perception of depth from cast shadows

Five- and 7-month-old infants viewed displays in which cast shadows provided information that two objects were at different distances. The 7-month-olds reached preferentially for the apparently nearer object under monocular-viewing conditions but exhibited no reaching preference under binocular-viewing conditions. These results indicate that 7-month-old infants perceive depth on the basis of cast shadows. The 5-month-olds did not reach preferentially for the apparently nearer object and, therefore, exhibited no evidence of sensitivity to cast shadows as depth information. In a second experiment, 5-month-olds reached preferentially for the nearer of two objects that were similar to those used in the first experiment but were positioned at different distances from the infant. This result indicated that 5-month-olds have the motor skills and motivation necessary to exhibit a reaching preference under the conditions of this study. The results are consistent with the hypothesis that depth perception based on cast shadows first appears between 5 and 7 months of age.     

Self-representation: searching for a neural signature of self-consciousness

Human self-consciousness operates at different levels of complexity and at least comprises five different levels of representational processes. These five levels are nonconceptual representation, conceptual representation, sentential representation, meta-representation, and iterative meta-representation. These different levels of representation can be operationalized by taking a first-person-perspective that is involved in representational processes on different levels of complexity. We refer to experiments that operationalize a first-person-perspective on the level of conceptual and meta-representational self-consciousness. Interestingly, these experiments show converging evidence for a recruitment of medial cortical and parietal regions during taking a first-person-perspective, even when operating on different degrees of complexity. These data lend support for the speculative hypothesis, that there exist a neural signature for human self-consciousness that is recruited independent from the degree of representational complexity to be performed.     

Are space and time automatically integrated in episodic memory?

The aim of the present study was to determine to what extent spatial and temporal features are automatically integrated during encoding in episodic memory. Both nameable and non-nameable stimuli were presented sequentially at different locations on a computer screen. Mixed and pure blocks of trials were used. In the mixed blocks participants were instructed to focus either on the spatial or the temporal order of the objects, as on the majority of the trials recall of this feature was tested (expected trials). However, on a few trials participants had to reproduce the other feature (unexpected trials). In the pure blocks either the spatial or the temporal order of the objects was tested on all trials. More errors were made on unexpected than on expected trials of the mixed blocks. Moreover, no primacy or recency effects were found when performance on the spatial task was plotted as a function of the temporal position. These results suggest that spatial information and temporal order information rely on separate encoding processes.     

Procedural memory in dissociative identity disorder: when can inter-identity amnesia be truly established?

In a serial reaction time task, procedural memory was examined in Dissociative Identity Disorder (DID). Thirty-one DID patients were tested for inter-identity transfer of procedural learning and their memory performance was compared with 25 normal controls and 25 controls instructed to simulate DID. Results of patients seemed to indicate a pattern of inter-identity amnesia. Simulators, however, were able to mimic a pattern of inter-identity amnesia, rendering the results of patients impossible to interpret as either a pattern of amnesia or a pattern of simulation. It is argued that studies not including DID-simulators or simulation-free memory tasks, should not be taken as evidence for (or against) amnesia in DID.     

Implicit learning of ignored visual context

Humans process a visual display more efficiently when they encounter it for a second time, showing learning of the display. This study tests whether implicit learning of complex visual contexts depends on attention. Subjects searched for a white target among black and white distractors. When the locations of the target and the attended set (white distractors) were repeated, search speed was enhanced, but when the locations of the target and the ignored set (black distractors) were repeated, search speed was unaffected. This suggests that the expression of learning depends on attention. However, during the transfer test, when the previously ignored set now was attended, it immediately facilitated performance. In contrast, when the previously attended set now was ignored, it no longer enhanced search speed. We conclude that the expression of visual implicit learning depends on attention but that latent learning of repeated information does not.     

Repairing inappropriately specified utterances: Revision or restart?

In two experiments, we investigated repair of inappropriately specified utterances (e.g.,blue square instead ofdark blue square) to determine whether speakers can simply revise a speech plan or must begin anew. In Experiment 1, speakers produced a prime utterance followed by a target utterance that differed from the prime in only one word, but in Experiment 2, they only planned the prime but produced the target. If speakers must repair by restarting, both situations would involve planning from scratch, with a possible benefit of residual activation. If they can repair by revising, though, only the first situation would involve planning from scratch, and the second situation would involve revision of a plan. The targets had either one word more (addition) or fewer (deletion) than the prime sentences. The restart hypothesis predicted that any cost of addition over deletion should be similar in the two experiments. In contrast, the revision hypothesis predicted an extra cost of addition in Experiment 2, because addition involves retrieval of an extra word. In support of the revision hypothesis, there was no difference between additions and deletions in Experiment 1, but in Experiment 2 additions took longer than deletions. We conclude that speakers can repair utterances by revising a speech plan.     

On the categorical nature of the semantic interference effect in the picture-word interference paradigm

Two picture-word interference experiments are reported in which the boundaries of the semantic interference effect are explored. In both experiments, participants named pictures (e.g., a picture of a car) that appeared with superimposed word distractors. Distractor words from the same semantic category as the word for the picture (e.g., CAR) produced semantic interference, whereas semantically related distractors from a different category (e.g.,Bumper) led to semantic facilitation. In Experiment 2, the semantic facilitation from semantically related distractors was replicated. These results indicate that a semantic relationship between picture and distractor does not necessarily lead to interference and in fact can lead to facilitation. In all but one case tested until now, a semantic relationship between picture and distractor has led to semantic facilitation. The implications of these results for the assumption that the semantic interference effect arises as a consequence of lexical competition are discussed.     

Evidence for an activation locus of the word-frequency effect in lexical decision

The authors report a lexical decision experiment designed to determine whether activation is the locus of the word-frequency effect. K. R. Paap and L. S. Johansen (1994) reported that word frequency did not affect lexical decisions when exposure durations were brief; they accounted for this by proposing that data-limited conditions prevented late-occurring verification processes. Subsequently, P. A. Allen, A. F. Smith, M. Lien, T. A. Weber, and D. J. Madden (1997) and K. R. Paap, L. S. Johansen, E. Chun, and P. Vonnahme (2000) reported additional evidence that word-frequency effects do and do not have an activation locus, respectively. The authors further tested this issue in a lexical decision experiment using data-limited procedures--predicted by verification models to eliminate word-frequency effects. The authors observed word-frequency effects using individually determined exposure durations that were only 1 screen cycle longer than the exposure duration that yielded chance performance. Word-frequency effects persisted even when an adjusted measure of performance was used.     

Effect of socioeconomic status on aphasia severity and recovery

Low levels of educational attainment and low socioeconomic status have been significantly linked to poor health and increased incidence of disease, including Alzheimer's disease and diseases of the cardiovascular, pulmonary, renal, and gastrointestinal systems. Our goal in the present study was to determine the degree to which educational level and socioeconomic status influence initial severity of aphasia and subsequent recovery. We evaluated the records of 39 persons with aphasia twice: at about 4 months and 103 months postonset. We found early severity of aphasia to be significantly greater for subjects in the lower educational and occupational groups. However, rate of recovery (the slope of the recovery curve) was the same regardless of educational or occupational status.