The Trouble with Cognitive Subtraction

Abstract

In this paper we present a critique of pure insertion. Pure insertion represents an implicit assumption behind many (but not all) studies that employ cognitive subtraction. The main contention is that pure insertion is not valid in relation to the neuronal instantiation of cognitive processes. Pure insertion asserts that there are no interactions among the cognitive components of a task. It is possible to evaluate and refute this assumption by testing explicitly for interactions using factorial experimental designs. It is proposed that factorial designs are more powerful than subtraction designs in characterizing cognitive neuroanatomy, precisely because they allow for interactions and eschew notions like pure insertion. In particular we suggest that the effect of a cognitive component (i.e., an effect that is independent of other components) is best captured by the main (activation) effect of that component and that the integration among components (i.e., the expression of one cognitive process in the context of another) can be assessed with the interaction terms. In this framework a complete characterization of cognitive neuroanatomy includes both regionally specific activations and regionally specific interactions. To illustrate our point we have used a factorial experimental design to show that inferotemporal activations, due to object recognition, are profoundly modulated by phonological retrieval of the object's name. This interaction implicates the inferotemporal regions in phonological retrieval, during object naming, despite the fact that phonological retrieval does not, by itself, activate this region. r

Semantic divergence and creative story generation: An fMRI investigation

“…Images were smoothed with a (12 mm FWHM) Gaussian kernel filter. The analysis of the functional imaging data entailed the creation of parametric maps representing a statistical assessment of hypothesized condition-specific activity using the general linear model approach [16]. A within-participants analysis was performed with identical models across participants.…”

Task-order coordination in dual-task performance and the lateral prefrontal cortex: an event-related fMRI study

“…The findings of these previous imaging studies suggested a specific role of the lateral prefrontal cortex (LPFC) for dual-task processing (D'Esposito, Detre, Alsop, Shin, Atlas, & Grossman, 1995;Goldberg et al, 1998;Schubert & Szameitat, 2003; but see Jiang, Saxe, & Kanwisher, 2004). Specifically, these studies compared the fMRI activation in dual-task blocks with the activation when participants performed the component tasks in single-task blocks, thereby employing the method of cognitive subtraction (Friston, Price, Fletcher, Moore, Frackowiak, & Dolan, 1996). The finding of an overadditive activation in prefrontal regions was interpreted as being related to additional cognitive demands present in the dual task, as compared to the summed demands of both single tasks.…”

Auditory processing abnormalities in schizotypal personality disorder: An fMRI experiment using tones of deviant pitch and duration

“…In fact, the hemodynamic effect of such thoughts using the subtraction method has been demonstrated in a tone task (Binder et al, 1999). Moreover, depending on the statistical approach, subtraction or other, results can differ markedly (Friston et al, 1996). The subtraction method assumes "pure insertion", that the cognitive process is "irrespective of the cognitive or physiological context" (Friston et al, 1996), an assumption which may not be valid.…”

“…Moreover, depending on the statistical approach, subtraction or other, results can differ markedly (Friston et al, 1996). The subtraction method assumes "pure insertion", that the cognitive process is "irrespective of the cognitive or physiological context" (Friston et al, 1996), an assumption which may not be valid. Indeed, the two fMRI papers in schizophrenia compared groups on standard and deviant tones separately, thus avoiding the difficulties of the subtraction method in an fMRI environment (Wible et al, 2001;Kircher et al, 2004).…”

“…1e). This has the benefit of making no assumption of "pure insertion" (Friston et al, 1996) and isolates the effect of hearing deviant tones "on top of" hearing all tones. In addition, this method may possibly minimize the hemodynamic effect of "task-unrelated thoughts" (Binder et al, 1999).…”