The verification of category and property statements

Context, categories and modality: Challenges for the Rumelhart model

Three issues are raised in this commentary. First, the mapping of semantic information into the different layers could be done in a more realistic way by using the Context layer to represent situational contexts. Second, a way to differentiate category membership information from other property information needs to be considered. Finally, the issue of modal knowledge is raised.

The categorical structure of semantic memory for famous people: a new approach using release from proactive interference

Memory for familiar people is essential to understand their identity and guide social interaction. Nevertheless, we know surprisingly little about the structure of such memory. Previous research has assumed that semantic memory for people has a categorical structure, but recently it was proposed that memory for people consists only of associations and lacks any categorical structure. Four experiments are reported that use a novel approach by adapting the 'release from proactive interference' (RPI) methodology for use with lists of famous names. Proactive interference occurs when items presented on successive trials are drawn from the same category. Recall can improve following a change to a different category. Sets of names were selected relating to aspects previously demonstrated, on the basis of reaction time data, to form a category (occupation) and a property (nationality) of celebrities (Johnston & Bruce, 1990). RPI was observed for a change at both levels of representation but was only present without explicitly cueing the change of set when the stimuli differed at the category level. At the property level, RPI was only evident when change of set was explicitly cued. RPI was absent at the set change in a novel, ad hoc distinction suggesting that the effect reflected the underlying memory structure.

Maintaining and updating semantic context in schizophrenia: an investigation of the effects of multiple remote primes

Conflicting findings regarding the ability of people with schizophrenia to maintain and update semantic contexts have been due, arguably, to vagaries within the experimental design employed (e.g. whether strongly or remotely associated prime-target pairs have been used, what delay between the prime and the target was employed, and what proportion of related prime-target pairs appeared) or to characteristics of the participant cohort (e.g. medication status, chronicity of illness). The aim of the present study was to examine how people with schizophrenia maintain and update contextual information over an extended temporal window by using multiple primes that were either remotely associated or unrelated to the target. Fourteen participants with schizophrenia and 12 healthy matched controls were compared across two stimulus onset asynchronies (SOAs) (short and long) and two relatedness proportions (RP) (high and low) in a crossed design. Analysis of variance statistics revealed significant two- and three-way interactions between Group and SOA, Group and Condition, SOA and RP, and Group, SOA and RP. The participants with schizophrenia showed evidence of enhanced remote priming at the short SOA and low RP, combined with a reduction in the time course over which context could be maintained. There was some sensitivity to biasing contextual information at the short SOA, although the mechanism over which context served to update information appeared to be different from that in the controls. The participants with schizophrenia showed marked performance decrements at the long SOA (both low and high RP). Indices of remote priming at the short (but not the long) SOA correlated with both clinical ratings of thought disorder and with increasing length of illness. The results support and extend the hypothesis that schizophrenia is associated with concurrent increases in tonic dopamine activity and decreases in phasic dopamine activity.

Associative and similarity-based processes in categorization decisions

Two experiments were directed at distinguishing associative and similarity-based accounts of systematic differences in categorization time for different items in natural categories. Experiment 1 investigated the correlation of categorization time with three measures of instance centrality in a category. Production frequency (PF), rated typicality, and familiarity from category norms for British participants (Hampton & Gardiner, 1983) were used to predict mean categorization times for 531 words in 12 semantic categories. PF and typicality (but not familarity) were found to make significant and independent contributions to categorization time. Error rates were related only to typicality (apart from errors made to ambiguous or unknown items). Experiment 2 provided a further dissociation of PF and typicality. Manipulating the difficulty of the task through the relatedness of the false items interacted primarily with the effect of typicality on categorization time, whereas, under conditions of easy discrimination, prior exposure to the category exemplars affected only the contribution of PF to the decision time. The dissociation of typicality and PF measures is interpreted as providing evidence that speeded categorization involves both retrieval of associations indexed by PF and a similarity-based decision process indexed by typicality.