Florian Hintz

Dysfunction of the auditory thalamus in developmental dyslexia

Developmental dyslexia, a severe and persistent reading and spelling impairment, is characterized by difficulties in processing speech sounds (i.e., phonemes). Here, we test the hypothesis that these phonological difficulties are associated with a dysfunction of the auditory sensory thalamus, the medial geniculate body (MGB). By using functional MRI, we found that, in dyslexic adults, the MGB responded abnormally when the task required attending to phonemes compared with other speech features. No other structure in the auditory pathway showed distinct functional neural patterns between the two tasks for dyslexic and control participants. Furthermore, MGB activity correlated with dyslexia diagnostic scores, indicating that the task modulation of the MGB is critical for performance in dyslexics. These results suggest that deficits in dyslexia are associated with a failure of the neural mechanism that dynamically tunes MGB according to predictions from cortical areas to optimize speech processing. This view on task-related MGB dysfunction in dyslexics has the potential to reconcile influential theories of dyslexia within a predictive coding framework of brain function.

Two cases of selective developmental voice-recognition impairments

Recognizing other individuals is an essential skill in humans and in other species. Over the last decade, it has become increasingly clear that person-identity recognition abilities are highly variable. Roughly 2% of the population has developmental prosopagnosia, a congenital deficit in recognizing others by their faces. It is currently unclear whether developmental phonagnosia, a deficit in recognizing others by their voices, is equally prevalent, or even whether it actually exists. Here, we aimed to identify cases of developmental phonagnosia. We collected more than 1,000 data sets from self-selected German individuals by using a web-based screening test that was designed to assess their voice-recognition abilities. We then examined potentially phonagnosic individuals by using a comprehensive laboratory test battery. We found two novel cases of phonagnosia: AS, a 32-year-old female, and SP, a 32-year-old male; both are otherwise healthy academics, have normal hearing, and show no pathological abnormalities in brain structure. The two cases have comparable patterns of impairments: both performed at least 2 SDs below the level of matched controls on tests that required learning new voices, judging the familiarity of famous voices, and discriminating pitch differences between voices. In both cases, only voice-identity processing per se was affected: face recognition, speech intelligibility, emotion recognition, and musical ability were all comparable to controls. The findings confirm the existence of developmental phonagnosia as a modality-specific impairment and allow a first rough prevalence estimate.

Encouraging prediction during production facilitates subsequent comprehension: Evidence from interleaved object naming in sentence context and sentence reading

Many studies have shown that a supportive context facilitates language comprehension. A currently influential view is that language production may support prediction in language comprehension. Experimental evidence for this, however, is relatively sparse. Here we explored whether encouraging prediction in a language production task encourages the use of predictive contexts in an interleaved comprehension task. In Experiment 1a, participants listened to the first part of a sentence and provided the final word by naming aloud a picture. The picture name was predictable or not predictable from the sentence context. Pictures were named faster when they could be predicted than when this was not the case. In Experiment 1b the same sentences, augmented by a final spill-over region, were presented in a self-paced reading task. No difference in reading times for predictive versus non-predictive sentences was found. In Experiment 2, reading and naming trials were intermixed. In the naming task, the advantage for predictable picture names was replicated. More importantly, now reading times for the spill-over region were considerable faster for predictive than for non-predictive sentences. We conjecture that these findings fit best with the notion that prediction in the service of language production encourages the use of predictive contexts in comprehension. Further research is required to identify the exact mechanisms by which production exerts its influence on comprehension.

Predictors of verb-mediated anticipatory eye movements in the visual world

Many studies have demonstrated that listeners use information extracted from verbs to guide anticipatory eye movements to objects in the visual context that satisfy the selection restrictions of the verb. An important question is what underlies such verb-mediated anticipatory eye gaze. Based on empirical and theoretical suggestions, we investigated the influence of 5 potential predictors of this behavior: functional associations and general associations between verb and target object, as well as the listeners’ production fluency, receptive vocabulary knowledge, and nonverbal intelligence. In 3 eye-tracking experiments, participants looked at sets of 4 objects and listened to sentences where the final word was predictable or not predictable (e.g., “The man peels/draws an apple”). On predictable trials only the target object, but not the distractors, were functionally and associatively related to the verb. In Experiments 1 and 2, objects were presented before the verb was heard. In Experiment 3, participants were given a short preview of the display after the verb was heard. Functional associations and receptive vocabulary were found to be important predictors of verb-mediated anticipatory eye gaze independent of the amount of contextual visual input. General word associations did not and nonverbal intelligence was only a very weak predictor of anticipatory eye movements. Participants’ production fluency correlated positively with the likelihood of anticipatory eye movements when participants were given the long but not the short visual display preview. These findings fit best with a pluralistic approach to predictive language processing in which multiple mechanisms, mediating factors, and situational context dynamically interact.

The Complexity of the Visual Environment Modulates Language-Mediated Eye Gaze

Three eye-tracking experiments investigated the impact of the complexity of the visual environment on the likelihood of word–object mapping taking place at phonological, semantic and visual levels of representation during language-mediated visual search. Dutch participants heard spoken target words while looking at four objects embedded in displays of different complexity and indicated the presence or absence of the target object. During filler trials the target objects were present, but during experimental trials they were absent and the display contained various competitor objects. For example, given the target word “beker” (beaker), the display contained a phonological (a beaver, bever), a shape (a bobbin, klos), a semantic (a fork, vork) competitor, and an unrelated distractor (an umbrella, paraplu). When objects were presented in simple four-object displays (Experiment 2), there were clear attentional biases to all three types of competitors replicating earlier research (Huettig and McQueen 2007). When the objects were embedded in complex scenes including four human-like characters or four meaningless visual shapes (Experiments 1, 3), there were biases in looks to visual and semantic but not to phonological competitors. In both experiments, however, we observed evidence for inhibition in looks to phonological competitors, which suggests that the phonological forms of the objects nevertheless had been retrieved. These findings suggest that phonological word–object mapping is contingent upon the nature of the visual environment and add to a growing body of evidence that the nature of our visual surroundings induces particular modes of processing during language-mediated visual search.