Semantic flow and its relation to controlled semantic retrieval deficits in the narrative production of people with aphasia.

Aphasia has had a profound influence on our understanding of how language is instantiated within the human brain. Historically, aphasia has yielded an in vivo model for elucidating the effects of impaired lexical-semantic access on language comprehension and production. Aphasiology has focused intensively on single word dissociations. Yet, less is known about the integrity of combinatorial semantic processes required to construct well-formed narratives. Here we addressed the question of how controlled lexical-semantic retrieval deficits (a hallmark of aphasia) might compound over the course of longer narratives. We specifically examined word-by-word flow of taxonomic vs. thematic semantic distance in the storytelling narratives of individuals with chronic post-stroke aphasia (n = 259) relative to age-matched controls (n = 203). We first parsed raw transcribed narratives into content words and computed inter-word semantic distances for every running pair of words in each narrative (N = 232,490 word transitions). The narratives of people with aphasia showed significant reductions in taxonomic and thematic semantic distance relative to controls. Both distance metrics were strongly predictive of offline measures of semantic impairment and aphasia severity. Since individuals with aphasia often exhibit perseverative language output (i.e., repetitions), we performed additional analyses with repetitions excluded. When repetitions were excluded, group differences in semantic distances persisted and thematic distance was still predictive of semantic impairment, although some findings changed. These results demonstrate the cumulative impact of deficits in controlled word retrieval over the course of narrative production. We discuss the nature of semantic flow between words as a novel metric of characterizing discourse and elucidating the nature of lexical-semantic access impairment in aphasia at multiword levels.

Olfactory language and semantic processing in anosmia: a neuropsychological case control study.

A longstanding debate within philosophy and neuroscience involves the extent to which sensory information is a necessary condition for conceptual knowledge. Much of our understanding of this relationship has been informed by examining the impact of congenital blindness and deafness on language and cognitive development. Relatively little is known about the "lesser" senses of smell and taste. Here we report a neuropsychological case-control study contrasting a young adult male (P01) diagnosed with anosmia (i.e. no olfaction) during early childhood relative to an age- and sex-matched control group. A structural MRI of P01's brain revealed profoundly atrophic/aplastic olfactory bulbs, and standardized smell testing confirmed his prior pediatric diagnosis of anosmia. Participants completed three language experiments examining comprehension, production, and subjective experiential ratings of odor salient words (e.g. sewer) and scenarios (e.g. fish market). P01's ratings of odor salience of single words were lower than all control participants, whereas his ratings on five other perceptual and affective dimensions were similar to controls. P01 produced unusual associations when cued to generate words that smelled similar to odor-neutral target words (e.g. ink → plant). In narrative picture description for odor salient scenes (e.g. bakery), P01 was indistinguishable from controls. These results suggest that odor deprivation does not overtly impair functional language use. However, subtle lexical-semantic effects of anosmia may be revealed using sensitive linguistic measures.

Neuromodulation of cursing in American English: A combined tDCS and pupillometry study.

Many neurological disorders are associated with excessive and/or uncontrolled cursing. The right prefrontal cortex has long been implicated in a diverse range of cognitive processes that underlie the propensity for cursing, including non-propositional language representation, emotion regulation, theory of mind, and affective arousal. Neurogenic cursing often poses significant negative social consequences, and there is no known behavioral intervention for this communicative disorder. We examined whether right vs. left lateralized prefrontal neurostimultion via tDCS could modulate taboo word production in neurotypical adults. We employed a pre/post design with a bilateral frontal electrode montage. Half the participants received left anodal and right cathodal stimulation; the remainder received the opposite polarity stimulation at the same anatomical loci. We employed physiological (pupillometry) and behavioral (reaction time) dependent measures as participants read aloud taboo and non-taboo words. Pupillary responses demonstrated a crossover reaction, suggestive of modulation of phasic arousal during cursing. Participants in the right anodal condition showed elevated pupil responses for taboo words post stimulation. In contrast, participants in the right cathodal condition showed relative dampening of pupil responses for taboo words post stimulation. We observed no effects of stimulation on response times. We interpret these findings as supporting modulation of right hemisphere affective arousal that disproportionately impacts taboo word processing. We discuss alternate accounts of the data and future applications to neurological disorders.

Building the perfect curse word: A psycholinguistic investigation of the form and meaning of taboo words.

Taboo words represent a potent subset of natural language. It has been hypothesized that "tabooness" reflects an emergent property of negative valence and high physiological arousal of word referents. Many taboo words (e.g., dick, shit) are indeed consistent with this claim. Nevertheless, American English is also rife with negatively valenced, highly arousing words the usage of which is not socially condemned (e.g., cancer, abortion, welfare). We evaluated prediction of tabooness of single words and novel taboo compound words from a combination of phonological, lexical, and semantic variables (e.g., semantic category, word length). For single words, physiological arousal and emotional valence strongly predicted tabooness with additional moderating contributions from form (phonology) and meaning (semantic category). In Experiment 2, raters judged plausibility for combinations of common nouns with taboo words to form novel taboo compounds (e.g., shitgibbon). A mixture of formal (e.g., ratio of stop consonants, length) and semantic variables (e.g., ± receptacle, ± profession) predicted the quality of novel taboo compounding. Together, these studies provide complementary evidence for interactions between word form and meaning and an algorithmic prediction of tabooness in American English. We discuss applications for models of taboo word representation.

Naming and Knowing Revisited: Eyetracking Correlates of Anomia in Progressive Aphasia.

Progressive naming impairment (i.e., anomia) is a core diagnostic symptom of numerous pathologies that impact anterior and inferior portions of the temporal lobe. For patients who experience such regional temporal lobe degeneration, patterns of language loss often parallel the degradation of semantic memory, an etiology of naming impairment known as semantic anomia. Previous studies of semantic anomia have focused extensively on the output of naming attempts by contrasting errors, omissions, and distortions as a function of item-level characteristics (e.g., prototypicality, semantic category). An alternative approach involves evaluating visual confrontation naming as the naming process unfolds. Techniques with high temporal resolution (e.g., eyetracking) offer a potentially sensitive mode of delineating the locus of impairment during naming. For example, a lexical retrieval disorder would hypothetically elicit normal gaze patterns associated with successful visual object recognition regardless of naming accuracy. In contrast, we hypothesize that semantic anomia would be distinguished by aberrant gaze patterns as a function of reduced top-down conceptually guided search. Here we examined visual object recognition during picture confrontation naming by contrasting gaze patterns time locked to stimulus onset. Patients included a cohort of patients with anomia associated with either primary progressive aphasia (N = 9) or Alzheimer's disease (N = 1) who attempted to name 200 pictures over the course of 18-24 months. We retrospectively isolated correct and incorrect naming attempts and contrasted gaze patterns for accurate vs. inaccurate attempts to discern whether gaze patterns are predictive of language forgetting. Patients tended to show a lower fixation count, higher saccade count, and slower saccade velocity for items that were named incorrectly. These results hold promise for the utility of eyetracking as a diagnostic and therapeutic index of language functioning.

The human task-evoked pupillary response function is linear: Implications for baseline response scaling in pupillometry.

The human task-evoked pupillary response provides a sensitive physiological index of the intensity and online resource demands of numerous cognitive processes (e.g., memory retrieval, problem solving, or target detection). Cognitive pupillometry is a well-established technique that relies upon precise measurement of these subtle response functions. Baseline variability of pupil diameter is a complex artifact that typically necessitates mathematical correction. A methodological paradox within pupillometry is that linear and nonlinear forms of baseline scaling both remain accepted baseline correction techniques, despite yielding highly disparate results. The task-evoked pupillary response (TEPR) could potentially scale nonlinearly, similar to autonomic functions such as heart rate, in which the amplitude of an evoked response diminishes as the baseline rises. Alternatively, the TEPR could scale similarly to the cortical hemodynamic response, as a linear function that is independent of its baseline. However, the TEPR cannot scale both linearly and nonlinearly. Our aim was to adjudicate between linear and nonlinear scaling of human TEPR. We manipulated baseline pupil size by modulating the illuminance in the testing room as participants heard abrupt pure-tone transitions (Exp. 1) or visually monitored word lists (Exp. 2). Phasic pupillary responses scaled according to a linear function across all lighting (dark, mid, bright) and task (tones, words) conditions, demonstrating that the TEPR is independent of its baseline amplitude. We discuss methodological implications and identify a need to reevaluate past pupillometry studies.

Frontotemporal stimulation modulates semantically-guided visual search during confrontation naming: A combined tDCS and eye tracking investigation.

Transcranial direct current stimulation (tDCS) was paired with eye tracking to elucidate contributions of frontal, temporoparietal and anterior temporal cortex to early visual search patterns during picture naming (e.g., rapid visual scanning to diagnostic semantic features). Neurotypical adults named line drawings of objects prior to and following tDCS in three separate sessions, each employing a unique electrode montage. The gaze data revealed montage by stimulation (pre/post) interaction effects characterized by longer initial visual fixations (mean difference = 89 ms; Cohen's d = .8) and cumulative fixation durations (mean difference = 98 ms; Cohen's d = .9) on key semantic features (e.g., the head of an animal) after cathodal frontotemporal stimulation relative to the pre-stimulation baseline. We interpret these findings as reflecting a tDCS-induced modulation of semantic contributions of the anterior temporal lobe(s) to top-down influences on object recognition. Further, we discuss implications for the optimization of tDCS for the treatment of anomia in aphasia.

Cathodal tDCS of the bilateral anterior temporal lobes facilitates semantically-driven verbal fluency.

In a verbal fluency task, a person is required to produce as many exemplars of a given category (e.g., 'animals', or words starting with 'f') as possible within a fixed duration. Successful verbal fluency performance relies both on the depth of search within semantic/phonological neighborhoods ('clustering') and the ability to flexibly disengage between exhausted clusters ('switching'). Convergent evidence from functional imaging and neuropsychology suggests that cluster-switch behaviors engage dissociable brain regions. Switching has been linked to a frontoparietal network dedicated to executive functioning and controlled lexical retrieval, whereas clustering is more commonly associated with temporal lobe regions dedicated to semantic and phonological processing. Here we attempted to modulate cluster-switch dynamics among neurotypical adults (N = 24) using transcranial direct current stimulation (tDCS) delivered at three sites: a) anterior temporal cortex; b) frontal cortex; and c) temporoparietal cortex. Participants completed letter-guided and semantic category verbal fluency tasks pre/post stimulation. Cathodal stimulation of anterior temporal cortex facilitated the total number of words generated and the number of words generated within clusters during semantic category verbal fluency. These neuromodulatory effects were specific to stimulation of the one anatomical site. Our findings highlight the role of the anterior temporal lobes in representing semantic category structure and support the claim that clustering and switching behaviors have distinct substrates. We discuss implications both for theory and application to neurorehabilitation.

A Neuropsychological Perspective on Abstract Word Representation: From Theory to Treatment of Acquired Language Disorders.

Natural languages are rife with words that describe feelings, introspective states, and social constructs (e.g., liberty, persuasion) that cannot be directly observed through the senses. Effective communication demands linguistic competence with such abstract words. In clinical neurological settings, abstract words are especially vulnerable to the effects of stroke and neurodegenerative conditions such as Alzheimer's disease. A parallel literature in cognitive neuroscience suggests that abstract and concrete words are at least partially neuroanatomically dissociable. Much remains to be learned about the nature of lexical-semantic deficits of abstract words and how best to promote their recovery. Here, we review contemporary theoretical approaches to abstract-concrete word representation with an aim toward contextualizing patient-based dissociations for abstract words. We then describe a burgeoning treatment approach for targeting abstract words and suggest a number of potential strategies for future interventions. We argue that a deeper understanding of is essential for informing language rehabilitation.