Plasticité cérébrale et comportement en modalité auditive chez la personne non-voyante

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal

Relevance of Spectral Cues for Auditory Spatial Processing in the Occipital Cortex of the Blind

We have previously shown that some blind individuals can localize sounds more accurately than their sighted counterparts when one ear is obstructed, and that this ability is strongly associated with occipital cortex activity. Given that spectral cues are important for monaurally localizing sounds when one ear is obstructed, and that blind individuals are more sensitive to small spectral differences, we hypothesized that enhanced use of spectral cues via occipital cortex mechanisms could explain the better performance of blind individuals in monaural localization. Using positron-emission tomography (PET), we scanned blind and sighted persons as they discriminated between sounds originating from a single spatial position, but with different spectral profiles that simulated different spatial positions based on head-related transfer functions. We show here that a sub-group of early blind individuals showing superior monaural sound localization abilities performed significantly better than any other group on this spectral discrimination task. For all groups, performance was best for stimuli simulating peripheral positions, consistent with the notion that spectral cues are more helpful for discriminating peripheral sources. PET results showed that all blind groups showed cerebral blood flow increases in the occipital cortex; but this was also the case in the sighted group. A voxel-wise covariation analysis showed that more occipital recruitment was associated with better performance across all blind subjects but not the sighted. An inter-regional covariation analysis showed that the occipital activity in the blind covaried with that of several frontal and parietal regions known for their role in auditory spatial processing. Overall, these results support the notion that the superior ability of a sub-group of early-blind individuals to localize sounds is mediated by their superior ability to use spectral cues, and that this ability is subserved by cortical processing in the occipital cortex

Effect of valproate on renal metabolism in the intact dog

Effect of valproate on renal metabolism in the intact dog. Valproate is an antiepileptic drug known to induce hyperammonemia in humans. This hyperammonemia might result from a reduced detoxification of ammonium in the liver and/or from an accelerated renal ammoniagenesis. Six dogs with normal acid-base equilibrium and eight dogs with chronic metabolic acidosis were infused with valproate directly into their left renal artery in order to obtain arterial concentrations around 3 to 4mM. The arterial ammonium concentration rose only in chronically acido tic dogs, whereas the lactate concentration and the lactate/pyruvate ratio increased in both groups. The urinary excretion of lactate and pyruvate increased markedly but the urinary excretion of other relevant metabolites remained minimal. Renal glutamine utilization and ammonium production were not changed by valproate administration in normal dogs but increased modestly in acidotic dogs. However, renal lactate utilization was drastically reduced and in fact, changed into a net production of lactate. Valproate strikingly reduced the renal cortical concentrations of glutamine, glutamate, alphaketoglutarate and citrate, and more modestly those of malate, oxaloacetate, aspartate, alanine and ATP. By contrast, the tissue lactate concentration and the lactate/pyruvate ratio were markedly increased. In experiments with brush border membrane vesicles, valproate inhibited the lactate transporter. These results suggest that high concentrations of valproate drastically inhibited the proximal reabsorption and the proximal and distal oxidation of lactate and pyruvate. Valproate probably became itself a significant energetic substrate for the kidney

Relationship between lactate and glutamine metabolism in vitro by the kidney: Differences between dog and rat and importance of alanine synthesis in the dog

Relationship between lactate and glutamine metabolism in vitro by the kidney: Differences between dog and rat and importance of alanine synthesis in the dog. Interaction between lactate (1 or 5 mM) and glutamine (1 or 5 mM) metabolism was studied with renal cortical slices incubated at a pH of 7.0 and obtained from acidotic (ammonium chloride) dogs and rats. The effect of amino-oxyacetate (0.2 mM), dichloroacetate (3 mM), and fluoroacetate (0.05 mM) was also studied. Significant differences were observed between dog and rat. In the dog, lactate had no effect on glutamine uptake and vice versa, but gluconeogenesis increased. Ammonia production, however, decreased by 13 to 21%, whereas a significant increase in alanine production was noted. In the rat, glutamine extraction and ammonia production dropped by 33% with 5 mM lactate. In contrast to the observation in the dog, no production of alanine was noted, but significant accumulation of glutamate took place. Amino-oxyacetate inhibited alanine production in the dog and reestablished ammoniagenesis, and it led to a marked decrement in the uptake of lactate and glucose production in both species. Dichloroacetate in the dog resulted in a reduction in pyruvate, alanine, glucose, and ammonia production while glutamate accumulation was observed. In both species, fluoroacetate stimulated glutamine uptake and ammonia production. With lactate alone, fluoroacetate decreased lactate uptake and glucose production. With both lactate and glutamine in the medium, fluoroacetate prevented any effect of lactate on ammoniagenesis. The present study demonstrates that lactate has a modest depressing effect on renal ammonia production by dog slices through increased synthesis of alanine and redistribution of nitrogen from glutamine. In the rat, the depressing effect of lactate on ammonia production in the alanine aminotransferase deficient kidney occurs through accumulation of glutamate. The data also reveal that oxidation of lactate to carbon dioxide is greater in the dog than it is in the rat, but that gluconeogenesis from lactate is more important in the rat.Relations entre les métabolismes du lactate et de la glutamine in vitro par le rein: Différences entre le chien et le rat et importance de la synthèse d'alanine chez le chien. L'interaction entre le métabolisme du lactate (1 ou 5 mM) et celui de la glutamine (1 ou 5 mM) a été étudiée sur des tranches de cortex rénal incubées à pH 7,0 et obtenues à partir de chiens ou de rats en acidose. L'effet de l'amino-oxyacétate (0,2 mM), du dichloroacétate (3 mM) et du fluoroacétate (0,05 mM) a aussi été étudié. Des différences significatives entre le rat et le chien ont été observées. Chez le chien, le lactate n'a pas d'effet sur la captation de glutamine, et réciproquement, mais la gluconéogenèse augmente. Cependant la production d'ammoniaque est diminuée de 13 à 21% alors qu'une augmentation significative de la production d'alanine est observée. Chez le rat, l'extraction de la glutamine et la production d'ammoniaque diminuent de 33% avec le lactate 5 mM. A l'opposé de ce qui est constaté chez le chien, il n'est pas observé de production d'alanine mais une accumulation significative de glutamate. L'amino-oxyacétate inhibe la production d'alanine chez le chien et restaure l'ammoniogenèse, cependant qu'il détermine une diminution importante de la captation de lactate et de la production de glucose dans les deux espèces. Le dichloroacétate a pour conséquence, chez le chien, une diminution de la production de pyruvate, d'alanine, de glucose et d'ammoniaque, cependant qu'une accumulation de glutamate est observée. Dans les deux espèces le fluoroacétate stimule la captation de glutamine et la production d'ammoniaque. Avec le lactate seul, le fluoroacétate diminue la captation de lactate et la production de glucose. Quand à la fois du lactate et de la glutamine sont ajoutés au milieu, le fluoroacétate empêche les effets du lactate sur l'ammoniogenèse. Ce travail démontre que le lactate a un effet dépresseur modeste sur la production rénale d'ammoniaque par les tranches de rein chez le chien par l'intermédiaire d'une augmentation de la synthèse de l'alanine et de la redistribution de l'azote à partir de la glutamine. Chez le rat, l'effet dépresseur du lactate sur la production d'ammoniaque dans le rein privé d'alanine amino-transférase s'exerce au moyen d'une accumulation de glutamate. Ces résultats révèlent que l'oxydation du lactate en CO2 est plus importante chez le chien que chez le rat alors que la gluconéogenèse à partir du lactate est plus importante chez le rat

Bilingualism and conversational understanding in young children

The purpose of the two experiments reported here was to investigate whether bilingualism confers an advantage on children’s conversational understanding. A total of 163 children aged 3 to 6 years were given a Conversational Violations Test to determine their ability to identify responses to questions as violations of Gricean maxims of conversation (to be informative and avoid redundancy, speak the truth, and be relevant and polite). Though comparatively delayed in their L2 vocabulary, children who were bilingual in Italian and Slovenian (with Slovenian as the dominant language) generally outperformed those who were either monolingual in Italian or Slovenian. We suggest that bilingualism can be accompanied by an enhanced ability to appreciate effective communicative responses

A visual processing advantage for young-adolescent deaf observers: Evidence from face and object matching tasks

It is unresolved whether the permanent auditory deprivation that deaf people experience leads to the enhanced visual processing of faces. The current study explored this question with a matching task in which observers searched for a target face among a concurrent lineup of ten faces. This was compared with a control task in which the same stimuli were presented upside down, to disrupt typical face processing, and an object matching task. A sample of young-adolescent deaf observers performed with higher accuracy than hearing controls across all of these tasks. These results clarify previous findings and provide evidence for a general visual processing advantage in deaf observers rather than a face-specific effect

Voice-based assessments of trustworthiness, competence, and warmth in blind and sighted adults

The study of voice perception in congenitally blind individuals allows researchers rare insight into how a lifetime of visual deprivation affects the development of voice perception. Previous studies have suggested that blind adults outperform their sighted counterparts in low-level auditory tasks testing spatial localization and pitch discrimination, as well as in verbal speech processing; however, blind persons generally show no advantage in nonverbal voice recognition or discrimination tasks. The present study is the first to examine whether visual experience influences the development of social stereotypes that are formed on the basis of nonverbal vocal characteristics (i.e., voice pitch). Groups of 27 congenitally or early-blind adults and 23 sighted controls assessed the trustworthiness, competence, and warmth of men and women speaking a series of vowels, whose voice pitches had been experimentally raised or lowered. Blind and sighted listeners judged both men’s and women’s voices with lowered pitch as being more competent and trustworthy than voices with raised pitch. In contrast, raised-pitch voices were judged as being warmer than were lowered-pitch voices, but only for women’s voices. Crucially, blind and sighted persons did not differ in their voice-based assessments of competence or warmth, or in their certainty of these assessments, whereas the association between low pitch and trustworthiness in women’s voices was weaker among blind than sighted participants. This latter result suggests that blind persons may rely less heavily on nonverbal cues to trustworthiness compared to sighted persons. Ultimately, our findings suggest that robust perceptual associations that systematically link voice pitch to the social and personal dimensions of a speaker can develop without visual input

Voice cues are used in a similar way by blind and sighted adults when assessing women’s body size

Humans’ ability to gauge another person’s body size from their voice alone may serve multiple functions ranging from threat assessment to speaker normalization. However, how this ability is acquired remains unknown. In two experiments we tested whether sighted, congenitally blind and late blind adults could accurately judge the relative heights of women from paired voice stimuli, and importantly, whether errors in size estimation varied with task difficulty across groups. Both blind (n = 56) and sighted (n = 61) listeners correctly judged women’s relative heights on approximately 70% of low difficulty trials, corroborating previous findings for judging men’s heights. However, accuracy dropped to chance levels for intermediate difficulty trials and to 25% for high difficulty trials, regardless of the listener’s sightedness, duration of vision loss, sex, or age. Thus, blind adults estimated women’s height with the same degree of accuracy, but also the same pattern of errors, as did sighted controls. Our findings provide further evidence that visual experience is not necessary for accurate body size estimation. Rather, both blind and sighted listeners appear to follow a general rule, mapping low auditory frequencies to largeness across a range of contexts. This sound-size mapping emerges without visual experience, and is likely very important for humans

The role of visual experience in the emergence of cross-modal correspondences

Cross-modal correspondences describe the widespread tendency for attributes in one sensory modality to be consistently matched to those in another modality. For example, high pitched sounds tend to be matched to spiky shapes, small sizes, and high elevations. However, the extent to which these correspondences depend on sensory experience (e.g. regularities in the perceived environment) remains controversial. Two recent studies involving blind participants have argued that visual experience is necessary for the emergence of correspondences, wherein such correspondences were present (although attenuated) in late blind individuals but absent in the early blind. Here, using a similar approach and a large sample of early and late blind participants (N=59) and sighted controls (N=63), we challenge this view. Examining five auditory-tactile correspondences, we show that only one requires visual experience to emerge (pitch-shape), two are independent of visual experience (pitch-size, pitch-weight), and two appear to emerge in response to blindness (pitch-texture, pitch-softness). These effects tended to be more pronounced in the early blind than late blind group, and the duration of vision loss among the late blind did not mediate the strength of these correspondences. Our results suggest that altered sensory input can affect cross-modal correspondences in a more complex manner than previously thought and cannot solely be explained by a reduction in visually-mediated environmental correlations. We propose roles of visual calibration, neuroplasticity and structurally-innate associations in accounting for our findings