Hierarchies, similarity, and interactivity in object recognition: "category-specific" neuropsychological deficits.

Category-specific impairments of object recognition and naming are among the most intriguing disorders in neuropsychology, affecting the retrieval of knowledge about either living or nonliving things. They can give us insight into the nature of our representations of objects: Have we evolved different neural systems for recognizing different categories of object? What kinds of knowledge are important for recognizing particular objects? How does visual similarity within a category influence object recognition and representation? What is the nature of our semantic knowledge about different objects? We review the evidence on category-specific impairments, arguing that deficits even for one class of object (e.g., living things) cannot be accounted for in terms of a single information processing disorder across all patients; problems arise at contrasting loci in different patients. The same apparent pattern of impairment can be produced by damage to different loci. According to a new processing framework for object recognition and naming, the hierarchical interactive theory (HIT), we have a hierarchy of highly interactive stored representations. HIT explains the variety of patients in terms of (1) lesions at different levels of processing and (2) different forms of stored knowledge used both for particular tasks and for particular categories of object.     

Global shape cannot be attended without object identification.

Whether the global shape of objects can be processed without accessing semantic or identity information was tested. Ss judged which of 2 fragmented forms had the same global shape as a reference stimulus. Matching stimuli could be physically identical, semantically related, or unrelated. The reference stimulus and nonmatching (distractor) form could be semantically related or unrelated. Similarity effects in the related condition were unconfounded with matches nameable and nonnameable forms. For nameable forms, related matching forms facilitated performance; a related distractor disrupted performance. Semantic interference was eliminated when nameable distractors were replaced with nonnameable partners; semantic similarity effects on matching were eliminated with a nonnameable reference stimulus and with inverted targets and distractors. Access to information concerning global shape does not normally occur without object identification.     

Connectionist models of neuropsychological disorders

Artificial neural networks ('connectionist models') embody aspects of real neuronal systems. But does studying the breakdown of performance in such models help us to understand cognitive impairments in humans following brain damage? Here we review recent attempts to capture different neuropsychological disorders using connectionist models with simulated lesions. We show how such lesion studies can be used to evaluate some of the standard assumptions made in neuropsychological research, concerning both double dissociations and associations between patterns of impairment. We also illustrate how lesioned models, like humans, can sometimes be more impaired on the easier of two tasks and demonstrate that connectionist models can incorporate forms of internal structure. Finally we discuss the utility of the models for understanding and predicting the effectiveness of different rehabilitation strategies. Future questions concern the role and possible development of internal structure within these models, whether the models can be generalized to larger-scale simulations, and whether they can accommodate higher-order linguistic disorders.     

Transient phonemic codes and immunity to proactive interference

Empirical data indicate that when memory for subspan lists of taxonomically related material is tested immediately after study, prior experience with lists involving the same material has no effect upon recall or recognition. In six experiments, we explored the possibility that immunity to proactive interference (PI) is related to discriminative information that is provided by transient phonemic codes. In these experiments, we manipulated the strength of phonemic codes as well as their presence or absence. Immunity to PI was found only when it was presumed that a phonemic representation of the target items existed and that information provided discriminative information. In all other cases, PI was observed. The finding that PI effects correspond with the manipulation of phonemic information in a principled fashion provides strong evidence for the role of phonemic codes in producing short-term PI effects.     

Categorizing chairs and naming pears: Category differences in object processing as a function of task and priming

Four experiments are reported examining the locus of structural similarity effects in picture recognition and naming with normal subjects. Subjects carried out superordinate categorization and naming tasks with picture and word forms of clothing, furniture, fruit, and vegetable exemplars. The main findings were as follows: (1) Responses to pictures of fruit and vegetables (\ldstructurally similar\rd objects) were slowed relative to pictures of clothing and furniture (\ldstructurally dissimilar\rd objects). This structural similarity difference was greater for picture naming than for superordinate categorization of pictures. (2) Structural similarity effects in picture naming were reduced by repetition priming. Repetition priming effects were equivalent from picture and word naming as prime tasks. (3) However, superordinate categorization of the prime did not produce the structural similarity effects on priming found for picture naming. Furthermore, such priming effects did not arise for picture or word categorization or for reading picture names as target tasks. It is proposed that structural similarity effects on priming object processing are located in processes mapping semantic representations of pictures to name representations required to select names for objects. Visually based competition between fruit and vegetables produces competition in name selection, which is reduced by priming the mappings between semantic and name representations.     

The Influence of Posttreatment Mutual Help Group Participation on the Friendship Networks of Substance Abuse Patients

The effect of 12-step mutual help groups (e.g., Narcotics Anonymous) on members' friendship networks has received little attention. This 1-year longitudinal study examined such effects in a sample of 2,337 male substance abuse inpatients, 57.7% of whom became significantly involved in 12-step activities (e.g., reading program literature, attending meetings) after treatment. An a priori model of the interplay of 12-step involvement and friendship networks was tested using structural equation modeling, and found to have excellent fit to the data. Twelve-step group involvement after treatment predicted better general friendship characteristics (e.g., number of close friends) and substance abuse-specific friendship characteristics (e.g., proportion of friends who abstain from drugs and alcohol) at follow-up. Results are discussed in terms of how mutual help group involvement benefits patients and how the self-help group evaluation paradigm should be broadened.     

Orthographic processing in visual word identification

A series of experiments is reported examining orthographic priming effects between briefly presented pairs of letter strings. The experiments investigate the effects of the number and position of letters shared by primes and targets, and the effects of prime-target length. Priming effects increase nonlinearly as a function of both the number and the position of shared letters, and they are dependent on the positions of letters relative to both the end positions in the string and to the identities of their nearest neighbours. There is little effect of absolute string length on priming. These priming effects can be distinguished from intrusion errors where letters from primes are reported in response to targets. An account of orthographic processing is outlined which attributes priming to cooperative interactions between coarse relative-position coded letter cluster representations activated by primes and targets. The implications of the findings for understanding other effects in word recognition and reading are discussed.     

Book reviews

Sutherland, S. (1989). Macmillan dictionary of psychology. London: Macmillan Reference Books. ISBN -333-38829-1. £ 29.95

Van Toller, S. & Dodd, G. H. (Eds.). (1988). Perfumery: the psychology and biology of fragrance. London: Chapman and Hall. Pp. 268. ISBN 0-412-30010-9. £ 35.00

Watt, R. J. (1987). Visual processing: Computational, psychophysical and cognitive resedrch. Hove: Lawrence Erlbaum Associates Ltd. Pp.160. ISBN 0-86377-081-9. £ 14.95/$ 26.95

Caplan, D. & Hildebrandt, N. (1988). disorders of syntactic comprehension. Cambridge, MA: MIT Press/Bradford Books. Pp. 340. ISBN 0-262-03132-9. £31.50     

Spreading suppression and the guidance of search by movement: Evidence from negative color carry-over effects

A growing number of studies have shown that significant impairments to search and selection can occur if the target item carries a feature of the irrelevant distractors currently being ignored Braithwaite, Humphreys, and Hodsoll (Journal of Experimental Psychology: Human Perception and Performance, 29, 758–778, 2003). However, these effects have been documented only when search has been extended over time (i.e., in preview search), and not in standard search displays with simultaneously presented items. Here, we present the first evidence that similar costs to selection can occur in simultaneous displays under appropriate circumstances. In the present experiment, participants searched a display for a moving target letter among static and moving distractors. Search efficiency was significantly enhanced for a moving target when half of the letters moved (and half remained static), allowing the static items to be excluded from search. However, if the moving target then shared its color with the irrelevant static items, significant costs emerged, relative to baselines. These results are consistent with the involvement of a general feature-based suppression mechanism in selection, operating over space as well as time.