The semantic organization of the animal category: evidence from semantic verbal fluency and network theory

Semantic memory is the subsystem of human memory that stores knowledge of concepts or meanings, as opposed to life-specific experiences. How humans organize semantic information remains poorly understood. In an effort to better understand this issue, we conducted a verbal fluency experiment on 200 participants with the aim of inferring and representing the conceptual storage structure of the natural category of animals as a network. This was done by formulating a statistical framework for co-occurring concepts that aims to infer significant concept-concept associations and represent them as a graph. The resulting network was analyzed and enriched by means of a missing links recovery criterion based on modularity. Both network models were compared to a thresholded co-occurrence approach. They were evaluated using a random subset of verbal fluency tests and comparing the network outcomes (linked pairs are clustering transitions and disconnected pairs are switching transitions) to the outcomes of two expert human raters. Results show that the network models proposed in this study overcome a thresholded co-occurrence approach, and their outcomes are in high agreement with human evaluations. Finally, the interplay between conceptual structure and retrieval mechanisms is discussed.     

Association splitting of the sexual orientation-OCD-relevant semantic network

There is little research on treating symptoms of sexual orientation-obsessive-compulsive disorder (SO-OCD). Semantic networks represent a new cognitive approach for understanding cognitive mechanisms of SO-OCD. Specifically, we tested whether the self-help cognitive technique of association splitting (AS) developed from this approach would be efficacious in reducing SO-OCD symptoms and thought suppression. One hundred and twenty heterosexual undergraduates (82 females, 38 males) were randomly assigned to either the AS or waitlist control group. At baseline and four weeks later, participants completed items assessing SO-OCD symptoms, measures of sexual obsessions and thought suppression, and an association task in which they generated associations to different cue words. Generated associations were coded based on SO-OCD relevance and emotional valence. Results indicated reductions in SO-OCD-relevant associations across levels of emotional valence and SO-OCD-irrelevant negative associations, and increases in SO-OCD-irrelevant positive and neutral associations, only in the AS group. Furthermore, there were reductions in SO-OCD symptoms, sexual obsessions, and thought suppression only in the AS group. Importantly, these findings were obtained with overall large effect sizes. AS appears to be an efficacious self-help technique in reducing SO-OCD symptoms, sexual obsessions, and thought suppression. Clinical implications, limitations, and suggestions for future research are discussed.     

Learning of novel semantic relationships via sudden comprehension is associated with a hippocampus-independent network

Sudden comprehension—or insight—during problem-solving can enhance learning, but the underlying neural processes are largely unknown. We investigated neural correlates of learning from sudden comprehension using functional magnetic resonance imaging and a verbal problem-solving task. Solutions and “solutions” to solvable and unsolvable verbal problems, respectively, were presented to induce sudden comprehension or continued incomprehension. We found activations of the hippocampus, medial prefrontal cortex (mPFC), amygdala, and striatum during sudden comprehension. Notably, however, mPFC and temporo-parietal neocortical structures rather than the hippocampus were associated with later learning of suddenly comprehended solutions. Moreover, difficult compared to easy sudden comprehension elicited midbrain activations and was associated with successful learning, pointing to learning via intrinsic reward. Sudden comprehension of novel semantic associations may constitute a special case of long-term memory formation primarily mediated by the mPFC, expanding our knowledge of its role in prior-knowledge-dependent memory.     

The comparability of verbal and nonverbal semantic differential scales in a joint semantic space

As an alternative to the verbal Semantic Differential (SD) measure of affective meaning systems, a nonverbal instrument-the Graphic Differential (GD)-has been developed for subject populations who have difficulty in verbal ratings. However, the factor structures of the pictographic scales have never been examined in a joint-verbal and nonverbal-semantic space as to whether their structures are equivalent to the affective systems defined by the verbal markers. The present study assessed this issue by reanalyzing the French (1977) data. The results indicated that when verbal SD and nonverbal GD scales were factor-analyzed separately, the three-dimensional structures of Evaluation (E), Potency (P), and Activity (A) were recaptured in both domains. However, when they were analyzed simultaneously in a joint semantic space, only the E and A dimensions were congruent. The GD P scales carried the meanings of denotative Heaviness, rather than the affective Potency. For future investigation, suggestion was made to systematically study both the affective and denotative semantic features within the contexts of nonverbal communciations.The authors made equal contributions toward the completion of the present research.     

The large-scale structure of semantic networks: statistical analyses and a model of semantic growth

We present statistical analyses of the large-scale structure of 3 types of semantic networks: word associations, WordNet, and Roget's Thesaurus. We show that they have a small-world structure, characterized by sparse connectivity, short average path lengths between words, and strong local clustering. In addition, the distributions of the number of connections follow power laws that indicate a scale-free pattern of connectivity, with most nodes having relatively few connections joined together through a small number of hubs with many connections. These regularities have also been found in certain other complex natural networks, such as the World Wide Web, but they are not consistent with many conventional models of semantic organization, based on inheritance hierarchies, arbitrarily structured networks, or high-dimensional vector spaces. We propose that these structures reflect the mechanisms by which semantic networks grow. We describe a simple model for semantic growth, in which each new word or concept is connected to an existing network by differentiating the connectivity pattern of an existing node. This model generates appropriate small-world statistics and power-law connectivity distributions, and it also suggests one possible mechanistic basis for the effects of learning history variables (age of acquisition, usage frequency) on behavioral performance in semantic processing tasks.     

How activation, entanglement, and searching a semantic network contribute to event memory

Free-association norms indicate that words are organized into semantic/associative neighborhoods within a larger network of words and links that bind the net together. We present evidence indicating that memory for a recent word event can depend on implicitly and simultaneously activating related words in its neighborhood. Processing a word during encoding primes its network representation as a function of the density of the links in its neighborhood. Such priming increases recall and recognition and can have long-lasting effects when the word is processed in working memory. Evidence for this phenomenon is reviewed in extralist-cuing, primed free-association, intralist-cuing, and single-item recognition tasks. The findings also show that when a related word is presented in order to cue the recall of a studied word, the cue activates the target in an array of related words that distract and reduce the probability of the target’s selection. The activation of the semantic network produces priming benefits during encoding, and search costs during retrieval. In extralist cuing, recall is a negative function of cue-to-distractor strength, and a positive function of neighborhood density, cue-to-target strength, and target-to-cue strength. We show how these four measures derived from the network can be combined and used to predict memory performance. These measures play different roles in different tasks, indicating that the contribution of the semantic network varies with the context provided by the task. Finally, we evaluate spreading-activation and quantum-like entanglement explanations for the priming effects produced by neighborhood density.     

Investigating semantic memory impairments: The contribution of semantic priming

Abstract

The semantic priming task is a valuable tool in the investigation of semantic memory impairments in patients with acquired disorders of language. This is because priming performance reflects automatic or implicit access to semantic information, unlike most other tests of semantic knowledge, which rely on explicit, voluntary access. Priming results are important for two main reasons: First, normal priming results may be observed in patients who perform poorly on other semantic memory tests, enabling us to distinguish between loss of, or damage to, information in semantic memory, and voluntary access to that information. Second, we can investigate the detailed pattern of loss and preservation of different types of semantic information, by charting the priming effects for different kinds of words, and different kinds of semantic relations between primes and targets.

We discuss the use of the priming task in this context, and address some of the theoretical and methodological criticisms that have been raised in connection with use of the priming task to address these issues. We then describe two recent studies in which we have employed semantic priming tasks, along with other more traditional methods, to investigate specific questions about the semantic memory deficits of three patients.     

How semantic memory structure and intelligence contribute to creative thought: a network science approach

The associative theory of creativity states that creativity is associated with differences in the structure of semantic memory, whereas the executive theory of creativity emphasises the role of top-down control for creative thought. For a powerful test of these accounts, individual semantic memory structure was modelled with a novel method based on semantic relatedness judgements and different criteria for network filtering were compared. The executive account was supported by a correlation between creative ability and broad retrieval ability. The associative account was independently supported, when network filtering was based on a relatedness threshold, but not when it was based on a fixed edge number or on the analysis of weighted networks. In the former case, creative ability was associated with shorter average path lengths and higher clustering of the network, suggesting that the semantic networks of creative people show higher small-worldness.     

The influence of semantic property and grammatical class on semantic selection

Research to-date has not successfully demonstrated consistent neural distinctions for different types of ambiguity or explored the effect of grammatical class on semantic selection. We conducted a relatedness judgment task using event-related functional magnetic resonance imaging (fMRI) to further explore these topics. Participants judged relatedness within word pairs. Consistent and inconsistent conditions were included along with filler items. Imaging results revealed a main effect of ambiguity in the dorsolateral prefrontal cortex (DLPFC) and parietal cortices. A main effect of grammatical class was observed in the parahippocampal and lingual gyri, and a main effect of consistency was found in the DLPFC, ventrolateral prefrontal cortex (VLPFC) and occipital cortices. Interactions among these factors were observed in the cingulate gyrus and motor cortices in addition to the DLPFC. These results suggest that both ambiguity type and grammatical class modulate semantic selection through different neural regions.     

The neurobiology of semantic memory

Semantic memory includes all acquired knowledge about the world and is the basis for nearly all human activity, yet its neurobiological foundation is only now becoming clear. Recent neuroimaging studies demonstrate two striking results: the participation of modality-specific sensory, motor, and emotion systems in language comprehension, and the existence of large brain regions that participate in comprehension tasks but are not modality-specific. These latter regions, which include the inferior parietal lobe and much of the temporal lobe, lie at convergences of multiple perceptual processing streams. These convergences enable increasingly abstract, supramodal representations of perceptual experience that support a variety of conceptual functions including object recognition, social cognition, language, and the remarkable human capacity to remember the past and imagine the future.     

The influence of response compatibility on a semantic classification task

An experiment was carried out in which Ss had to decide whether or not a target word was a member of a prespecified semantic category. Poorly representative, or low conjoint frequency (LCF) exemplars were accepted less rapidly than representative, or high conjoint frequency (HCF) exemplars. This effect was considerably enhanced by requiring an incompatible response in which the Ss were asked to say ‘No’ when the target was a member of the category. The results show that the category membership judgement is a natural affirmative, and that the semantic distance effect of conjoint frequency has a magnitude dependent upon the processing demands of the task in which it is measured. The results are discussed in relation to theories of the mechanisms of category membership judgements. It is suggested that the influence of compatibility may be in load sharing between activation of a response rule and the judgement task per se.     

A constraint on eliminating semantic priming by repeating a prime

Repeated semantic primes have been shown to generate an additive semantic priming effect when those primes are different words, but repetition priming of the prime seems to eliminate semantic priming of lexical decisions for reasons that are not clear. These studies replicated this effect but also showed that repetition priming of the prime does not eliminate semantic priming with a longer lag between the repeated primes. The implications of these results for understanding the basic effect are discussed.     

The semantic organization and classification of fourteen words by aphasic patients

The purpose of this study was to assess both conceptual knowledge and classification skills in nonfluent and fluent aphasia by focusing on the aphasics' appreciation of class and function relations. The results illustrated that fluent and nonfluent aphasics appreciated both class and function relations. However, further study revealed that even though the fluent aphasic may know the function of an item, he is impaired in his ability to use this information. The nonfluent aphasics also illustrated this tendency not to use their knowledge about function, but to a lesser extent and without the consistency found in the performance of fluent aphasics.     

The semantic side of decision making

The research reported in this paper follows the perspective that decision making is a meaningful act that conveys information. Furthermore, the potential meanings associated with decision options may affect the decisions themselves. This idea is examined in the contexts of compensation, donation, and exchange. In general, judgments were relation dependent and meaning dependent. Furthermore, the results show nonmonotonicities and limited substitutability in a pattern that challenges straightforward ways of mapping decisions onto a common currency of utility.     

The selective impairment of semantic memory

The selective impairment of semantic memory is described in three patients with diffuse cerebrallesions. These patients, selected on the basis of a failure to recognize or identify common objects (agnosia for objects), were investigated in detail. In particular, their perceptual, language and memory functions were assessed, and the limits and properties of their recognition difficulties explored.

It was found that knowledge of pictorial representations of objects, and of words, was impaired or impoverished, and in both instances knowledge of subordinate categories was more vulnerable than superordinate categories. Evidence is presented that this impairment of semantic memory cannot be accounted for by intellectual impairment, sensory or perceptual deficits, or expressive language disorder. The implications of damage to the semantic memory system for the operation of other cognitive systems, in particular short and long-term memory functions, are considered. Some tentative evidence for the structural basis for a hierarchically organized modality-specific semantic memory system is discussed.