Active Role of Self-Sustained Neural Activity on Sensory Input Processing: A Minimal Theoretical Model

A growing body of work has demonstrated the importance of ongoing oscillatory neural activity in sensory processing and the generation of sensorimotor behaviors. It has been shown, for several different brain areas, that sensory-evoked neural oscillations are generated from the modulation by sensory inputs of inherent self-sustained neural activity (SSA). This letter contributes to that strand of research by introducing a methodology to investigate how much of the sensory-evoked oscillatory activity is generated by SSA and how much is generated by sensory inputs within the context of sensorimotor behavior in a computational model. We develop an abstract model consisting of a network of three Kuramoto oscillators controlling the behavior of a simulated agent performing a categorical perception task. The effects of sensory inputs and SSAs on sensory-evoked oscillations are quantified by the cross product of velocity vectors in the phase space of the network under different conditions (disconnected without input, connected without input, and connected with input). We found that while the agent is carrying out the task, sensory-evoked activity is predominantly generated by SSA (93.10%) with much less influence from sensory inputs (6.90%). Furthermore, the influence of sensory inputs can be reduced by 10.4% (from 6.90% to 6.18%) with a decay in the agent's performance of only 2%. A dynamical analysis shows how sensory-evoked oscillations are generated from a dynamic coupling between the level of sensitivity of the network and the intensity of the input signals. This work may suggest interesting directions for neurophysiological experiments investigating how self-sustained neural activity influences sensory input processing, and ultimately affects behavior.

Categorical Perception: A Groundwork for Deep Learning

Classification is one of the major tasks that deep learning is successfully tackling. Categorization is also a fundamental cognitive ability. A well-known perceptual consequence of categorization in humans and other animals, categorical per ception, is notably characterized by a within-category compression and a between-category separation: two items, close in input space, are perceived closer if they belong to the same category than if they belong to different categories. Elaborating on experimental and theoretical results in cognitive science, here we study categorical effects in artificial neural networks. We combine a theoretical analysis that makes use of mutual and Fisher information quantities and a series of numerical simulations on networks of increasing complexity. These formal and numerical analyses provide insights into the geometry of the neural representation in deep layers, with expansion of space near category boundaries and contraction far from category boundaries. We investigate categorical representation by using two complementary approaches: one mimics experiments in psychophysics and cognitive neuroscience by means of morphed continua between stimuli of different categories, while the other introduces a categoricality index that, for each layer in the network, quantifies the separability of the categories at the neural population level. We show on both shallow and deep neural networks that category learning automatically induces categorical perception. We further show that the deeper a layer, the stronger the categorical effects. As an outcome of our study, we propose a coherent view of the efficacy of different heuristic practices of the dropout regularization technique. More generally, our view, which finds echoes in the neuroscience literature, insists on the differential impact of noise in any given layer depending on the geometry of the neural representation that is being learned, that is, on how this geometry reflects the structure of the categories.

Categorical Perception of Chinese Lexical Tones by Late Second Language Learners With High Proficiency: Behavioral and Electrophysiological Measures

Purpose Although acquisition of Chinese lexical tones by second language (L2) learners has been intensively investigated, very few studies focused on categorical perception (CP) of lexical tones by highly proficient L2 learners. This study was designed to address this issue with behavioral and electrophysiological measures. Method Behavioral identification and auditory event-related potential (ERP) components for speech discrimination, including mismatch negativity (MMN), N2b, and P3b, were measured in 23 native Korean speakers who were highly proficient late L2 learners of Chinese. For the ERP measures, both passive and active listening tasks were administered to examine the automatic and attention-controlled discriminative responses to within- and across-category differences for carefully chosen stimuli from a lexical tone continuum. Results The behavioral task revealed native-like identification function of the tonal continuum. Correspondingly, the active oddball task demonstrated larger P3b amplitudes for the across-category than within-category deviants in the left recording site, indicating clear CP of lexical tones in the attentive condition. By contrast, similar MMN responses in the right recording site were elicited by both the across- and within-category deviants, indicating the absence of CP effect with automatic phonological processing of lexical tones at the pre-attentive stage even in L2 learners with high Chinese proficiency. Conclusion Although behavioral data showed clear evidence of categorical perception of lexical tones in proficient L2 learners, ERP measures from passive and active listening tasks demonstrated fine-grained sensitivity in terms of response polarity, latency, and laterality in revealing different aspects of auditory versus linguistic processing associated with speech decoding by means of largely implicit native language acquisition versus effortful explicit L2 learning.

Categorical Perception of Mandarin Pitch Directions by Cantonese-Speaking Musicians and Non-musicians

Purpose: This study is to investigate whether Cantonese-speaking musicians may show stronger CP than Cantonese-speaking non-musicians in perceiving pitch directions generated based on Mandarin tones. It also aims to examine whether musicians may be more effective in processing stimuli and more sensitive to subtle differences caused by vowel quality.Methods: Cantonese-speaking musicians and non-musicians performed a categorical identification and a discrimination task on rising and falling continua of fundamental frequency generated based on Mandarin level, rising and falling tones on two vowels with nine duration values.Results: Cantonese-speaking musicians exhibited a stronger categorical perception (CP) of pitch contours than non-musicians based on the identification and discrimination tasks. Compared to non-musicians, musicians were also more sensitive to the change of stimulus duration and to the intrinsic F0 in pitch perception in pitch processing.Conclusion: The CP was strengthened due to musical experience and musicians benefited more from increased stimulus duration and were more efficient in pitch processing. Musicians might be able to better use the extra time to form an auditory representation with more acoustic details. Even with more efficiency in pitch processing, musicians' ability to detect subtle pitch changes caused by intrinsic F0 was not undermined, which is likely due to their superior ability to process temporal information. These results thus suggest musicians may have a great advantage in learning tones of a second language.

Categorical encoding of speech sounds: beyond auditory cortices

What processes lead to categorical perception of speech sounds? Investigation of this question is hampered by the fact that categorical speech perception is normally confounded by acoustic differences in the stimulus. By using ambiguous sounds, however, it is possible to dissociate acoustic from perceptual stimulus representations. We used a binaural integration task, where the inputs to the two ears were complementary so that phonemic identity emerged from their integration into a single percept. Twenty-seven normally hearing individuals took part in an fMRI study in which they were presented with an ambiguous syllable (intermediate between /da/ and /ga/) in one ear and with a meaning-differentiating acoustic feature (third formant) in the other ear. Multi-voxel pattern searchlight analysis was used to identify brain areas that consistently differentiated between response patterns associated with different syllable reports. By comparing responses to different stimuli with identical syllable reports and identical stimuli with different syllable reports, we disambiguated whether these regions primarily differentiated the acoustics of the stimuli or the syllable report. We found that BOLD activity patterns in the left anterior insula (AI), the left supplementary motor cortex, the left ventral motor cortex and the right motor and somatosensory cortex (M1/S1) represent listeners' syllable report irrespective of stimulus acoustics. The same areas have been previously implicated in decision-making (AI), response selection (SMA), and response initiation and feedback (M1/S1). Our results indicate that the emergence of categorical speech sounds implicates decision-making mechanisms and auditory-motor transformations acting on sensory inputs.

Persepsi Mahasiswa Tingkat Menengah terhadap Perubahan Frekuensi dan Waktu Titik Lekuk Nada Turun-Naik Bahasa Mandarin

<p><strong>The tone is a phonetic characteristic of Chinese which is very important to master because it has a meaning-distinguishing function. For Indonesian students, Chinese tone, especially tone 2 and tone 3 is quite difficult to master both in perception and pronunciation. This study aims to measure the level of sensitivity and type of perception of students with intermediate level Chinese language proficiency in distinguishing tone 2 and tone 3. The tone or sound stimulus used in this study are fluctuating tones (</strong><strong>降升调</strong><strong>) which is the basic form of the second and third tones by varying the frequency and time of the curve point. The research method used is the experimental method, a research instrument based on a test. The results showed that changes in the high frequency and time of curve point in fluctuating sound stimulus had a significant effect. Respondents were more sensitive to changes in sound stimuli with the independent variable time of the curve point compared to the high frequency. The type of respondent's perception of the sound stimulus with the time-independent variable at the curve point is categorized as categorical perception. Meanwhile, the respondent's perception of the sound stimulus with the high-frequency independent variable at the curve point is classified as the continuous perception</strong></p><p><strong>Keywords –</strong><em> </em><em>C</em><em>ategorical perception, </em><em>C</em><em>ontinuous perception,</em><em> </em><em>Chinese</em><em> phonetic, </em><em>Chinese</em><em> tone</em><strong> </strong></p>