Modularity Hypothesis Research Articles

Through a Glass Darkly: Schizophrenia and Functional Brain Imaging

Abstract: Functional neuroimaging frequently assumes anatomically and functionally specific "modules" in the brain. Schizophrenia, which is challenging in many ways, also challenges modularity. A prominent example of a modular hypothesis links working memory (WM) deficits in schizophrenia with decreased function in the prefrontal cortex, a result confirmed in several studies. Nonetheless, these studies are systematically blind to the alternative possibility that schizophrenia reflects dysfunction in broader, more distributed systems of the brain. However, to establish hypotheses about distributed cognition in health and illness requires new interpretations of functional neuroimaging. Modularity can be assessed by large-scale meta-analyses of neuroimaging studies, illustrated here through the on-line database, Brainmap (www.brainmap.org). The apparent association of WM and prefrontal cortex fades when one considers all areas engaged in WM, and all tasks associated with prefrontal cortex. In addition, several global measures of connectivity based in functional neuroimaging may provide measures of distributed dysfunction. For example, Independent Component Analysis reveals unusual oscillations in distributed networks in patients with schizophrenia.

Optimal modularity: a demonstration of the evolutionary advantage of modular architectures

Modularity is an important concept in evolutionary theorizing but lack of a consistent definition renders study difficult. Using the generalized NK-model of fitness landscapes, we differentiate modularity from decomposability. Modular and decomposable systems are both composed of subsystems, but in the former, these subsystems are connected via interface standards, while in the latter, subsystems are completely isolated. We derive the optimal level of modularity, which minimizes the time required to globally optimize a system, both for the case of two-layered systems and for the general case of multi-layered hierarchical systems containing modules within modules. This derivation supports the hypothesis of modularity as a mechanism to increase the speed of evolution. Our formal definition clarifies the concept of modularity and provides a framework and an analytical baseline for further research.

The Attributive/Referential Distinction, Pragmatics, Modularity of Mind and Modularization

In this paper I deal with the attributive/referential distinction. After reviewing the literature on the issue, I adopt Jaszczolt's view based on default semantics. I relate her view to Sperber and Wilson's Principle of Relevance. I argue in favour of the modularity hypothesis in connection with pragmatic interpretations. I also discuss the issue of modularization à la Karmiloff-Smith in connection with default inferences and, in particular, referential readings of NPs. I reply to some considerations by Cummings and use data from referential/attributive uses of NPs to show that the modularity hypothesis is defensible.

Dominance plausible rule and transitivity

In qualitative decision theory, a very natural way for defining preference relations over policies (acts) -functions from a set S of states to a set X of consequences- is by using the so called Dominance Plausible Rule. In this context we need a relation > over X and a relation ⊵ over P(S) (the subsets of S). Then we define ≥ as follows: f ≥ g, ⇔ [f > g] ⊵ [g > f], where [f > g] denotes the set {s ∈ S : f(s) > g(s)g}. In many cases > is a modular relation and ⊵ is a total preorder. A quite rational and desirable property for the relation over policies is transitivity. In general, the relation ≥ defined by the Dominance Plausible Rule is not transitive in spite of the transitivity of ⊵. In this work we characterize the properties of the relation ⊵ forcing the relation ≥ over policies to be transitive. All this under the hypothesis of modularity of the relation >.

QUANTITATIVE GENETICS OF SHAPE IN CRICKET WINGS: DEVELOPMENTAL INTEGRATION IN A FUNCTIONAL STRUCTURE

The role of developmental and genetic integration for evolution is contentious. One hypothesis states that integration acts as a constraint on evolution, whereas an alternative is that developmental and genetic systems evolve to match the functional modularity of organisms. This study examined a morphological structure, the cricket wing, where developmental and functional modules are discordant, making it possible to distinguish the two alternatives. Wing shape was characterized with geometric morphometrics, quantitative genetic information was extracted using a full-sibling breeding design, and patterns of developmental integration were inferred from fluctuating asymmetry of wing shape. The patterns of genetic, phenotypic, and developmental integration were clearly similar, but not identical. Heritabilities for different shape variables varied widely, but no shape variables were devoid of genetic variation. Simulated selection for specific shape changes produced predicted responses with marked deflections due to the genetic covariance structure. Three hypotheses of modularity according to the wing structures involved in sound production were inconsistent with the genetic, phenotypic, or developmental covariance structure. Instead, there appears to be strong integration throughout the wing. The hypothesis that genetic and developmental integration evolve to match functional modularity can therefore be rejected for this example.

Variation in N-V compound verbs in Japanese

This paper shows that in Japanese there is a compounding of a verb with its argument that results in a verbal compound (VC) with a [+V] feature, contrary to the prediction made by Sugioka (2002). Based on the hypothesis of modularity in word formation (cf. Kageyama, 1993). Sugioka (2002) shows that there are two types of N-V compounds in Japanese: N-V compounds with a [−V] feature, which are formed through the incorporation of the internal argument of the verb, while those involving an adjunct are formed at the level of LCS and can be regarded as complex predicates with a [+V] feature. In this paper, I argue that the motivation of forming another type of N-V compounds, namely the VC with a [+V] feature involving the argument, is different from either of these types and lies in the foregrounding of a certain participant in the event. I propose an analysis for N-V compounding in the framework of Generative Lexicon, which assumes that the qualia structure of the nonhead can provide the compound with an argument which is not selected by the head verb. This supports the assumption that the qualia structure should be taken as a reservoir of semantic information which can contribute to determining the lexical semantic feature of the coinage.

Phenotypic Integration Without Modularity: Testing Hypotheses About the Distribution of Pleiotropic Quantitative Trait Loci in a Continuous Space

Theories of phenotypic integration have relied heavily on the concept of modularity in order to model the ways in which traits in an organism correlate and covary. Recent investigations suggest that, while some functional and developmental processes may be morphologically and ontogenetically localized, and thus modular in a developmental sense, there is a great deal of overlap among these influences on patterns of integration in the adult form. This can result in blurry boundaries between hypothesized modules constructed to test hypotheses about phenotypic integration. This investigation tests hypotheses about the contribution of pleiotropic quantitative trait loci (QTL) to phenotypic integration in the mouse mandible without using a priori categorical hypotheses about which traits constitute a module. We ask two main questions: (1) Are the effects of pleiotropic QTL localized to highly correlated traits or more spread out among traits than one might expect by chance? (2) Does the pattern of trait influence when all pleiotropic QTL are considered together deviate from what we might expect if QTL affect traits without regard for the correlations among traits? We find that a large proportion of pleiotropic QTL affect traits that are more highly correlated than we expect by chance with the remainder having effects that are distributed as if by chance. Furthermore, the overall distribution of the effects of pleiotropic QTL differs significantly from the null distribution of no association between pleiotropic effects on traits and correlations among traits. The main modular hypothesis used by earlier studies often does not predict the distribution of sets of traits sharing a common QTL. These results suggest that there is a clear tendency for pleiotropic effects of QTL to be localized but that the localization may be best thought of as occurring in a continuous space rather being clustered in discrete modules.

“Discourse features”, syntactic displacement and the status of contrast

Contrast and its syntactic correlates, various contrastive focus and contrastive topic movements, are investigated from the perspective of a hypothesis constraining the set of formal features active in the computational system (C HL). I propose a Strong Modularity Hypothesis for Discourse Features, according to which no discourse notion can be encoded by formal features. In contrast to currently prevalent cartographic approaches, it claims that only truth-conditional notions may constitute formal features active in the C HL. Movements corresponding to non-truth-conditional notions, such as notions of information structure, must thus be interface phenomena, rather than driven by a feature-checking mechanism. To test this hypothesis, the paper investigates (a) the so-called contrastive focus movement, well-known from Hungarian, involving exhaustive identification, and (b) a distinct class of widely attested contrast-related movements – contrastive topic and contrastive focus movements – that involve a closed set whose members are explicit in the context, and have no entailment of exhaustivity. The distinct types of discourse-related, and in particular contrast-related, movements analyzed are argued to be due, respectively, to (a) an independent quantificational operator of the C HL, such as the truth-conditional maximality operator motivated for Hungarian, or (b) interface effects, such as accommodation of nuclear stress assignment or facilitation of the mapping of syntactic representations to information structure.

A STATISTICAL FRAMEWORK FOR TESTING MODULARITY IN MULTIDIMENSIONAL DATA

Modular variation of multivariate traits results from modular distribution of effects of genetic and epigenetic interactions among those traits. However, statistical methods rarely detect truly modular patterns, possibly because the processes that generate intramodular associations may overlap spatially. Methodologically, this overlap may cause multiple patterns of modularity to be equally consistent with observed covariances. To deal with this indeterminacy, the present study outlines a framework for testing a priori hypotheses of modularity in which putative modules are mathematically represented as multidimensional subspaces embedded in the data. Model expectations are computed by subdividing the data into arrays of variables, and intermodular interactions are represented by overlapping arrays. Covariance structures are thus modeled as the outcome of complex and nonorthogonal intermodular interactions. This approach is demonstrated by analyzing mandibular modularity in nine rodent species. A total of 620 models are fit to each species, and the most strongly supported are heuristically modified to improve their fit. Five modules common to all species are identified, which approximately map to the developmental modules of the mandible. Within species, these modules are embedded within larger "super-modules," suggesting that these conserved modules act as building blocks from which covariation patterns are built.

Massive Modularity and Brain Evolution

Quartz (2002) argues that some recent findings about the evolution of the brain (Finlay and Darlington 1995) are inconsistent with evolutionary psychologists’ massive modularity hypothesis. In substance, Quartz contends that since the volume of the neocortex evolved in a concerted manner, natural selection did not act on neocortical systems independently of one another, which is a necessary condition for cognition to be massively modular. In this article, I argue that Quartz's argument fails to undermine the massive modularity hypothesis.

Evolutionary Psychology Versus Fodor: Arguments For and Against the Massive Modularity Hypothesis

Evolutionary psychologists tend to view the mind as a large collection of evolved, functionally specialized mechanisms, or modules. Cosmides and Tooby (1994) have presented four arguments in favor of this model of the mind: the engineering argument, the error argument, the poverty of the stimulus argument, and combinatorial explosion. Fodor (2000) has discussed each of these four arguments and rejected them all. In the present paper, we present and discuss the arguments for and against the massive modularity hypothesis. We conclude that Cosmides and Tooby's arguments have considerable force and are too easily dismissed by Fodor.

Reconstructing Reason and Representation.

In Reconstructing Reason and Representation, Murray Clarke offers a detailed study of the philosophical implications of evolutionary psychology. In doing so, he offers new solutions to key problems in epistemology and philosophy of mind, including misrepresentation and rationality. He proposes a naturalistic approach to reason and representation that is informed by evolutionary psychology, and, expanding on the massive modularity thesis advanced in work by Leda Cosmides and John Tooby, argues for a modular, adapticist account of misrepresentation and knowledge. Just as the reliability of representation can be defended on the basis of an account of the proper function of cognitive modularity, misrepresentation can be explained through an appeal to the gap theory, by noting the divergence between the proper and actual domains of cognitive modules in a massively modular mind.Clarke argues for an externalist, modular reliabilism by suggesting that evolution has equipped us with generally reliable inferential systems even if they do not always produce true beliefs. He argues that reliable deductive and inductive inference occurs only when cognitive modules deal with actual domains that are sufficiently similar to their proper domains. This psychologically informed, naturalized adapticism leads to the suggestion that knowledge is a set of natural kinds housed in the modules of a massively modular mind. Typically, the proper function of these cognitive modules is to provide us with truths that enable us to satisfy our basic biological needs. Beyond reasoning modules, other cognitive modules discussed include the ability to orient ourselves in space, and our abilities with language, numbers, object reasoning, and social understanding. Clarke also defends Cosmides and Tooby's massive modularity hypothesis against such critics as Jerry Fodor by demonstrating that these critics consistently misrepresent Cosmides and Tooby's position.

Modularidad e innatismo: una crítica a la noción sustancial de módulo *

In the Philosophy of Cognitive Science, it is a common held view that the modularity hypothesis for cognitive mechanisms and the innateness hypothesis for mental contents are conceptually independent. In this paper I distinguish between substantial and deflationist modularity as well as between substantial and deflationist innatism, and I analyze whether the conceptual independence between substantial modularity and innatism holds. My conclusion will be that if what is taken into account are the essential properties of the substantial modules, i.e. domain specificity and informational encapsulation, then it seems to be such independence. However, if what is taken into account is the function of the substantial modules, then it seems to be a conceptual connection from modularity to substantial innateness.

Familiarity accentuates gaze cuing in women but not men

Gaze cuing, the tendency to shift attention in the direction other individuals are looking, is hypothesized to depend on a distinct neural module. One expectation of such a module is that information processing should be encapsulated within it. Here, we tested whether familiarity, a type of social knowledge, penetrates the neural circuits governing gaze cuing. Male and female subjects viewed the face of an adult male looking left or right and then pressed a keypad to indicate the location of a target appearing randomly left or right. Responses were faster for targets congruent with gaze direction. Moreover, gaze cuing was stronger in females than males. Contrary to the modularity hypothesis, familiarity enhanced gaze cuing, but only in females. Sex differences in the effects of familiarity on gaze cuing may reflect greater adaptive significance of social information for females than males.

Precise spatial relationships between mossy fibers and climbing fibers in rat cerebellar cortical zones.

Classically, mossy fiber and climbing fiber terminals are regarded as having very different spatial distributions in the cerebellar cortex. However, previous anatomical studies have not studied these two major cerebellar inputs with sufficient resolution to confirm this assumption. Here, we examine the detailed pattern of collateralization of both types of cerebellar afferent using small injections of the bidirectional tracer cholera toxin b subunit into the posterior cerebellum. The cortical and zonal location of these injections was characterized by mapping climbing fiber field potentials, the distribution of retrogradely labeled olivary neurons, and the intrinsic zebrin pattern of Purkinje cells. Labeled climbing fiber collaterals were distributed as longitudinal strips and were always accompanied by clusters of labeled mossy fiber rosettes in the subjacent granular layer. Two- and three-dimensional reconstructions and quantitative analysis showed that mossy fibers also collateralized to other stripe-like regions usually below Purkinje cells with the same zebrin-positive or zebrin-negative characteristics as that of the injection site and associated climbing fiber collaterals. The distribution of retrogradely labeled neurons in two major sources of mossy fibers, the lateral reticular and basilar pontine nuclei, revealed interlobular and some interzonal differences. These data indicate that nonadjacent cerebellar zones, sharing the same climbing fiber input and zebrin identity, also share a common mossy fiber input. Other cerebellar cortical regions that receive collaterals from the same mossy fibers usually also have the same zebrin signature. Together with the distribution of neurons in precerebellar centers, the findings suggest a revision of the modular hypothesis for information processing in the cerebellar cortex.

Cognitive architecture and descent with modification

Against a background of recent progress in developmental neuroscience, some of which has been taken as challenging to the modularity hypothesis of Fodor (1983), this article contrasts two competing conceptions of modularity: sui generis modularity, according to which modules are treated as independent neurocognitive entities that owe nothing to one another, and descent-with-modification modularity, according to which current cognitive modules are understood to be shaped by evolutionary changes from ancestral cognitive modules. I argue that sui generis modularity is incompatible with a range of data, from the co-occurrence of deficits to the patterns of activation in neuroimaging studies, but that same range of data is compatible with descent-with-modification modularity. Furthermore, I argue that the latter conception of modularity may have important implications for the practice and conception of fields such as developmental disorders and linguistics.

Anecdotes, data and regulatory modules

Beginning in the late 1980s, Eric Davidson's group at Cal Tech developed a modularity hypothesis of developmental gene regulation, showing that in an expanding number of cases, particular aspects of development were governed by compact 'modules' of transcription factor binding sites (TFBSs), and that these modules were separable, complex and interconnected. Davidson made no attempt to further generalize the hypothesis, but others took up the idea, transported it out of development and extended it to a general rule of clustering. Despite such misbegotten origins, the 'extended' modularity hypothesis--that TFBSs in general tend to come in compact clusters--has been highly productive, yet it has never been challenged with a large, diverse and unbiased dataset to see how universal it actually is. The aim of the present paper is to do so. Applying human-mouse-rat phylogenetic footprinting to neighbourhoods of a diverse set of TFBSs, including both developmental and non-developmental signals, we find that the extended hypothesis holds in at least 93.5% of cases. Based on this particular sample, we found a mean module length of 609 nucleotides containing, on an average, 24.5 presumptive regulatory signals of length greater than 5 and averaging 8.5 nucleotides each.

DEFINING A MEETING PLACE: MODULARITY IN DEVELOPMENT AND EVOLUTION

Modularity describes the general idea that biological systems at many hierarchical levels are not uniformly interconnected, but rather composed of subparts: discrete elements of the phenotype possess a degree of internal integration stronger than their external connectivity, and maintain their identity and function independent of the context in which they are embedded. The behavior or function of a module reflects the integration, not simply the sum, of its constituents; and although modules are biological individuals (Hull 1980; Roth 1991), they must also show external connectivity and interaction (an individual in isolation is not a module; Bolker 2000). We readily recognize as modules individual body parts such as bones, limbs, or segments; DNA sequences that constitute specific genes or regulatory motifs; and process modules (Gilbert and Bolker 2000) ranging from courtship displays to intercellular signal transduction pathways. Evolutionary biology relies on a working assumption that it is both feasible and biologically justifiable to view the phenotype as modular, treating different aspects (whether structures or genes) as largely dissociable entities that respond to selection in a relatively independent manner. The success of this paradigm offers strong evidence that the hypothesis of modularity accords well with biological reality. In fact, most of the analytical tools for describing the evolution of organisms rest (explicitly or otherwise) on the premise that one can delineate distinct characters (Bolker 2000). Beyond its central importance to evolutionary biology, the concept of modularity has been described as a potential meeting place for evolutionary and developmental biologists, and thus a promising bridge for interdisciplinary studies of evolutionary developmental biology (EDB or evo-devo; Von Dassow and Munro 1999; Bolker 2000; Gass and Bolker 2003). In support of that claim, Gerhard Schlosser and Gunter Wagner convened a workshop comprising developmental biologists studying specific model systems, evolutionary biologists interested in the origins and long-term significance of modularity, and philosophers and theorists with ideas about how to think about the concept. The resulting volume demonstrates that modularity is indeed an interesting and fruitful way to think about development, evolution and their interrelationship-and that we still have a long way to go. The diverse collection of papers also highlights the complexities of studying a concept that, while intuitively obvious, is surprisingly difficult to define in a precise and universally acceptable way.

The influence of contextual contrast on syntactic processing: evidence for strong-interaction in sentence comprehension

The present study compares the processing of unambiguous restrictive and non-restrictive relative clauses (RCs) within both a null context and a supportive discourse using a self-paced reading methodology. Individuals read restrictive RCs more slowly than non-restrictive RCs in a null context, but processed restrictive RCs faster than non-restrictive RCs in supportive context, resulting in an interaction between context and RC type. These results provide evidence for two theoretical points. First, principles analogous to those in referential theory [Altmann G. T. M., & Steedman, M. (1988). Interaction with context during human sentence processing. Cognition, 30, 191–238; Crain, S., & Steedman, M. (1985). On not being led up the garden path: The use of context by the psychological parser. In D. Dowty, L. Karttunnen, A. Zwicky (Eds.), Natural language parsing. Cambridge, UK: Cambridge University Press] apply not only in resolving ambiguity but also in processing unambiguous sentences. Second, the discourse context can guide and facilitate interpretive processing. This result suggests that intrasentential factors such as syntax are not autonomous from contextual processing, contrary to the modularity hypothesis [Fodor, J. A. (1983). Modularity of mind. Cambridge, MA: MIT Press].

Characterization of the Phd Repressor-Antitoxin Boundary

The P1 plasmid addiction operon (a classic toxin-antitoxin system) encodes Phd, an unstable 73-amino-acid repressor-antitoxin protein, and Doc, a stable toxin. It was previously shown by deletion analysis that the N terminus of Phd was required for repressor activity and that the C terminus was required for antitoxin activity. Since only a quarter of the protein or less was required for both activities, it was hypothesized that Phd might have a modular organization. To further test the modular hypothesis, we constructed and characterized a set of 30 point mutations in the third and fourth quarters of Phd. Four mutations (PhdA36H, V37A, I38A, and F44A) had major defects in repressor activity. Five mutations (PhdD53A, D53R, E55A, F56A, and F60A) had major defects in antitoxin activity. As predicted by the modular hypothesis, point mutations affecting each activity belonged to disjoint, rather than overlapping, sets and were separated rather than interspersed within the linear sequence. A final deletion experiment demonstrated that the C-terminal 24 amino acid residues of Phd (preceded by a methionine) retained full antitoxin activity.