It is widely accepted that color is perceived categorically. Categorical perception of color can be defined as the tendency to discriminate colors that are from different categories easier, quicker and more accurately than colors that are from the same category. The present study investigated whether brain activity patterns verifies the concept of categorical color perception, an instantiation of top-down influences on low-level perception. Participants performed a color discrimination task on color pairs. Three categories of color pairs are defined in the green-blue region as follows. One of the pairs was specified as cross-category pair by choosing one color from green side of the green-blue boundary and the other color from blue side. The other two pairs were featured as within-category pairs by choosing two shades of green for within-green pair and two shades of blue for within-blue pair. Crucially, the pairs varied only in hue dimension and the physical distance between each of three pairs was set to 10 degrees in CIE LCh space. Pairs on the screen are displayed adjacently or with gaps in between, to further investigate the effect of space in color discrimination. Correct responses, reaction times and fMRI BOLD signals are recorded. Behavioral findings yielded a decrementing pattern from green to blue region challenging the prediction of categorical perception argument that performance is better at green-blue boundary than both within green and blue regions. Behavioral findings also indicated that adjacent display of colors facilitated color discrimination when compared to display of colors with spatial gaps. Brain activity patterns indicated that separate neural processes might underlie these distinct behavioral differences. Although standardized with respect to the color metric, the three categories of our experiment might have involved differences with respect to difficulty levels and memory requirements. Brain activity differences reported in the within-green condition versus cross-category condition are focused on Frontal Eye Fields and Fusiform Gyrus, which is seem to be modulated by Frontal Eye Field activity / increased activation in these regions is related to enhanced visual performance and higher scores, which is consistent with significantly better performance in within-green discrimination than cross-category discrimination. For the same contrast, Parahippocampal Gyrus and Precuneus activations suggest better visual recall and behavioral improvement due to more efficient maintenance in spatial working memory for within-green discrimination than cross-category discrimination. Brain activity differences reported in the within-blue condition versus cross-category condition is focused on Superior Temporal Gyrus, which is involved in color discrimination having the role of color memory. When within-green and within-blue conditions are compared, there was differential activation in the Fusiform Gyrus, and this is the only brain activity which might be attributed to a categorical effect. This comparison also yielded activity in Medial Frontal and Superior Frontal regions concerning more confident perceptual decisions and improved performance on within-green discrimination than within-blue discrimination. In addition, spatial separation of stimuli entailed more cognitive resources to color discrimination than adjacent stimuli as suggested by Cuneus and Lingual Gyrus activations. Overall, to the best of our knowledge our study is the first to investigate the neural framework for color perception, which revealed that color perception might involve several complex sub-processes that activate memory and attention.

Turkish speakers differentiate the blue region of color spectrum into mavi (blue) and lacivert (dark blue) / whereas non-Turkish speakers in this study had only one color term in the blue region. The present study aimed to explore the predictions of the Linguistic Relativity Hypothesis. Operationally, Categorical Perception (CP) effects were used. In Experiment 1, Turkish speakers performed a naming task to determine an average category boundary between mavi and lacivert. In Experiment 2, both Turkish and non-Turkish speakers&rsquo / color-difference detection thresholds were estimated on the average boundary as well as within the mavi and lacivert categories. The thresholds were also estimated in the green region, in which both groups had only one color term. 2-TAFC method, which eliminates the effects of memory or labeling and isolates the perceptual processes, was used to estimate the thresholds. Turkish speakers, and not non-Turkish speakers, were predicted to show CP effects only in the blue region: thresholds should be lower on the boundary than within-category. The result revealed that Turkish speakers&rsquo / color-difference detection thresholds were lower than those of non-Turkish speakers both in the blue and the green regions. The difference in the green region does not rule out the LRH. It is possible that this difference resulted from the limitations of the study. Finally, in Experiment 3, Turkish speakers&rsquo / thresholds were also estimated on their individual boundaries. The patterns of the thresholds revealed by Experiment 3 were similar to the pattern of the thresholds in Experiment 2.

Children at risk for reading problems also have difficulty perceiving critical differences in speech sounds (Breier et al., 2004; Edwards, Fox, & Rogers, 2003; de- Gelder & Vroomen, 1998). These children rely more heavily on context than the acoustic qualities of sound to facilitate word reading. Dialect use, such as African American English (AAE) may influence literacy development in similar ways. Dialect use has been shown to affect speech sound processing and can even result in spelling errors (Kohler, et al., in press). The purpose of this study is to determine if children who speak AAE process cues indicative of final consonant voicing differently than children who speak a more mainstream dialect of English. Twenty-six typically developing children in grades K-2 who spoke either AAE or a more mainstream American English dialect participated. The speech stimuli consisted of nonsense productions of vowel + plosive consonant. These stimuli were systematically altered by changing the vowel and stop-gap closure duration simultaneously, which resulted in the final consonant changing from a voiced consonant, like “ib”, to a voiceless consonant, like “ip”. Two tasks were developed: a continuum task where the child had to indicate when the stimuli changed in voicing and a same-different task which involved determining if two stimuli were identical in voicing or not. No significant differences between groups were found for dialect use or grade for the same/different task. In the continuum task, chi-square analyses revealed significant differences in response patterns attributable to dialect and grade. In addition, a significant consonant by speaker interaction was found for mean ratings. Correlations between mean continuum rating and phonological awareness composites were not significant. In conclusion, it was evident that children who speak AAE present with differences in their perception of final consonants in VC nonsense syllables. This finding suggests the dialect speakers may be using different cues to make judgments regarding the speech signal, or that the speakers of AAE have a less mature ability to extract fine phonetic detail due to the influence of their dialect (Baran & Seymour, 1979). More research is warranted to determine the exact role that dialect plays.

Dans le cas de perte auditive neurosensorielle, la biomécanique cochléaire se trouve modifiée et les phénomènes actifs liés aux cellules ciliées sont altérés. Si les conséquences sur la baisse de sensibilité, les capacités de sélectivité fréquentielle ou la compréhension de la parole dans le bruit sont bien connus, la perception de la hauteur tonale peut également être modifiée suite à une perte neurosensorielle. Cette thèse se propose d’étudier la perception de la hauteur à travers quatre approches chez des sujets présentant une surdité neurosensorielle. La première étude s’intéresse à la diplacousie et a montré que ce phénomène était bien plus fréquent que ce que l’on pouvait imaginer. Les résultats ont montré que la perception était en règle générale plus aiguë sur l’oreille la plus lésée. La seconde étude propose une mesure catégorielle de la tonie. Les résultats ont montré que pour une même fréquence, les malentendants percevaient un son comme plus aigu que les normo-entendants. La troisième étude traite de la correspondance d’octave et de l’écoute de la musique. Les résultats montrent que la perte auditive est corrélée avec la perception de l’octave. La quatrième étude s’intéresse à la perception catégorielle des fricatives non-voisées. Les résultats montrent que la frontière catégorielle est décalée vers les fréquences graves ce qui semble être le reflet d’une perception plus aigue de ces phonèmes. Ces résultats d’expériences de psychoacoustique vont dans le sens des études menées sur des animaux montrant une modification de la carte tonotopique cochléaire et des fréquences caractéristiques des neurones lors d’une atteinte neurosensorielle. Ces observations pourraient conduire à une meilleure prise en charge des malentendants et à l’élaboration de nouveaux algorithmes sur les futures aides auditives / In the case of sensorineural hearing loss, the cochlear mechanism is modified and the active phenomena linked to the hair cells are altered. If the effects on decreased sensitivity, frequency selectivity, or speech in noise intelligibility are well known, the perception of pitch can also be altered following a neurosensory hearing loss. This thesis proposes to study the perception of pitch with four approaches in subjects with neurosensory hearing loss. The first study focuses on diplacusis and has shown that this phenomenon is much more frequent than one could imagine. The results showed that perception was generally higher on the worse ear. The second study proposes a categorical measure of pitch. The results showed that for the same frequency, the hearing-impaired perceived a sound higher than the normal hearing listeners. The third study is about octave matching and listening to music. The results show that hearing loss correlates with the octave matching frequency. The fourth study focuses on the categorical perception of voiceless fricatives. The results show that the categorical boundary is shifted towards the low frequencies, which seems to reflect a higher perception of these phonemes. These results of psychoacoustic experiments are consistent with the studies carried out on animals showing a modification of the cochlear tonotopic map and the characteristic frequencies of the neurons in case of a neurosensory hearing loss. These observations could lead to better care for the hearing impaired and to the development of new algorithms on future hearing aids

During spoken language comprehension, listeners transform continuous acoustic cues into categories (e.g. /b/ and /p/). While longstanding research suggests that phoneme categories are activated in a gradient way, there are also clear individual differences, with more gradient categorization being linked to various communication impairment like dyslexia and specific language impairments (Joanisse, Manis, Keating, & Seidenberg, 2000; López-Zamora, Luque, Álvarez, & Cobos, 2012; Serniclaes, Van Heghe, Mousty, Carré, & Sprenger-Charolles, 2004; Werker & Tees, 1987). Crucially, most studies have used two-alternative forced choice (2AFC) tasks to measure the sharpness of between-category boundaries. Here we propose an alternative paradigm that allows us to measure categorization gradiency in a more direct way. We then use this measure in an individual differences paradigm to: (a) examine the nature of categorization gradiency, (b) explore its links to different aspects of speech perception and other cognitive processes, (c) test different hypotheses about its sources, (d) evaluate its (positive/negative) role in spoken language comprehension, and (e) assess whether it can be modified via training. Our results provide validation for this new method of assessing phoneme categorization gradiency and offer valuable insights into the mechanisms that underlie speech perception.

Although there is a wealth of knowledge on categorization early in life, there are still many unanswered questions about the nature of category representation in infancy. For example, it is unclear whether infants are sensitive to boundaries between complex categories, such as types of animals, or whether young infants exhibit such sensitivity without explicit experience in the lab. Using a morphing technique, we linearly altered the category composition of images and measured 6.5-month-olds’ attention to pairs of animal faces that either did or did not cross the categorical boundary, with the stimuli in each pair being equally dissimilar from one another across the two types of image pairs. Results indicated that infants dichotomize the continua between cats and dogs and between cows and otters, but only when the images are presented in their canonical, upright orientations. These findings demonstrate a propensity to dichotomize early in life that could have implications for social categorizations, such as race and gender.

The purpose of this study is to determine whether children with autism recognize the same perceptual voicing boundaries of stop consonants as normally developing children of the same age group. This was explored using three groups of participants: ten children with autism between the ages of 8-14, five typically developing children between the ages of 8-14, and five typically developing seven-year-old children. Children in all groups listened to initial stop consonant syllables with voicing contrasts, with voiced and voiceless cognates presented. The initial consonants were altered along a voice onset time continuum within the typically perceived boundaries of each consonant. Participants were instructed to select the box containing the letter of the initial consonant they perceive when they hear each syllable. Results revealed greater difference between the responses of the children with autism when compared with the older control group, than when compared with the younger children. The responses of the children with autism were more similar to those of the children in the second control group. This could be indicative of a delay in the children with autism of perception of the categorical boundaries along the dimension of voice onset time compared to typical children's perception of these consonants.

Adults perceive basic emotional facial expressions as discrete categories using categorical perception. Within categorical perception, discrimination of facial emotional expressions is better for between category faces than within category faces. In this thesis, I examined the developmental trajectory of categorical perception in early childhood. I also examined the relationship between sensitivity to physical differences in facial emotional expressions and the use of emotion labels in toddlers. In Chapter 2, I found that infants before 12-months failed to discriminate between category faces along a happy-sad continuum. In contrast, evidence suggest that 9- and 12-month old infants categorically perceived faces along a happy-angry continuum. These findings suggest that categorical perception may not develop concurrently for all emotions. In Chapter 3, I found that toddlers by 26-months of age categorically perceived faces along a happy-sad continuum. These results highlight the long developmental trajectory of categorical perception of facial emotional expressions across early childhood. In Chapter 4, I found a relationship between perceptual sensitivity to physical differences between happy and sad faces, and the emotion vocabulary size in 26-month-olds. This relationship suggests that learning about emotions may utilize information from multiple domains, and that learning in one domain may influence the development of another. The perception of facial emotional expressions is an essential component of early social emotional development. Categorical perception is a mechanism that aids in organizing complex social information from faces into actionable categories. The research in this thesis advances our understanding of early social perceptual development and the process that allow us to successfully navigate in the social world. / Dissertation / Doctor of Philosophy (PhD) / Humans are experts at reading faces. Specifically, they are capable of interpreting complex social information from faces, including emotions, and using this information to navigate social situations. In order to organize facial emotional information, humans use a mechanism called categorical perception to quickly and efficiently sort facial emotional information into discrete categories. Inferences can be made about members within a category, which aids in the prediction and production appropriate behaviours. However, there has been limited research into the development of categorical perception in early childhood. The key goal of this thesis was to develop infant and toddler appropriate methodologies that capture the development categorical perception. In this thesis, I found that categorical perception does not develop uniformly across all ages and between different emotions. Results suggest that perceptual sensitivity to differences in facial emotional expression may be influenced by the use of emotion labels, or vice versa.

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