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Does Auditory Feedback Perturbation Influence Categorical Perception of Vowels?

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Speech perception and production are bidirectionally related, and they influence each other. The purpose of this study was to better understand the relationship between speech perception and speech production. It is known that applying auditory perturbations during speech production causes

Speech perception and production are bidirectionally related, and they influence each other. The purpose of this study was to better understand the relationship between speech perception and speech production. It is known that applying auditory perturbations during speech production causes subjects to alter their productions (e.g., change their formant frequencies). In other words, previous studies have examined the effects of altered speech perception on speech production. However, in this study, we examined potential effects of speech production on speech perception. Subjects completed a block of a categorical perception task followed by a block of a speaking or a listening task followed by another block of the categorical perception task. Subjects completed three blocks of the speaking task and three blocks of the listening task. In the three blocks of a given task (speaking or listening) auditory feedback was 1) normal, 2) altered to be less variable, or 3) altered to be more variable. Unlike previous studies, we used subject’s own speech samples to generate speech stimuli for the perception task. For each categorical perception block, we calculated subject’s psychometric function and determined subject’s categorical boundary. The results showed that subjects’ perceptual boundary remained stable in all conditions and all blocks. Overall, our results did not provide evidence for the effects of speech production on speech perception.

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2019-05

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Compensatory Responses During Unexpected Vowel Perturbations

Description

During speech, the brain is constantly processing and monitoring speech output through the auditory feedback loop to ensure correct and accurate speech. If the speech signal is experimentally altered/perturbed while speaking, the brain compensates for the perturbations by changing speech

During speech, the brain is constantly processing and monitoring speech output through the auditory feedback loop to ensure correct and accurate speech. If the speech signal is experimentally altered/perturbed while speaking, the brain compensates for the perturbations by changing speech output in the opposite direction of the perturbations. In this study, we designed an experiment that examined the compensatory responses in response to unexpected vowel perturbations during speech. We applied two types of perturbations. In one condition, the vowel /ɛ/ was perturbed toward the vowel /æ/ by simultaneously shifting both the first formant (F1) and the second formant (F2) at 3 different levels (.5=small, 1=medium, and 1.5=large shifts). In another condition, the vowel /ɛ/ was perturbed by shifting F1 at 3 different levels (small, medium, and large shifts). Our results showed that there was a significant perturbation-type effect, with participants compensating more in response to perturbation that shifted /ɛ/ toward /æ/. In addition, we found that there was a significant level effect, with the compensatory responses to level .5 being significantly smaller than the compensatory responses to levels 1 and 1.5, regardless of the perturbation pathway. We also found that responses to shift level 1 and shift level 1.5 did not differ. Overall, our results highlighted the importance of the auditory feedback loop during speech production and how the brain is more sensitive to auditory errors that change a vowel category (e.g., /ɛ/ to /æ/).

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2019-05

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Somatosensory Modulation during Speech Planning

Description

Previous studies have found that the detection of near-threshold stimuli is decreased immediately before movement and throughout movement production. This has been suggested to occur through the use of the internal forward model processing an efferent copy of the motor

Previous studies have found that the detection of near-threshold stimuli is decreased immediately before movement and throughout movement production. This has been suggested to occur through the use of the internal forward model processing an efferent copy of the motor command and creating a prediction that is used to cancel out the resulting sensory feedback. Currently, there are no published accounts of the perception of tactile signals for motor tasks and contexts related to the lips during both speech planning and production. In this study, we measured the responsiveness of the somatosensory system during speech planning using light electrical stimulation below the lower lip by comparing perception during mixed speaking and silent reading conditions. Participants were asked to judge whether a constant near-threshold electrical stimulation (subject-specific intensity, 85% detected at rest) was present during different time points relative to an initial visual cue. In the speaking condition, participants overtly produced target words shown on a computer monitor. In the reading condition, participants read the same target words silently to themselves without any movement or sound. We found that detection of the stimulus was attenuated during speaking conditions while remaining at a constant level close to the perceptual threshold throughout the silent reading condition. Perceptual modulation was most intense during speech production and showed some attenuation just prior to speech production during the planning period of speech. This demonstrates that there is a significant decrease in the responsiveness of the somatosensory system during speech production as well as milliseconds before speech is even produced which has implications for speech disorders such as stuttering and schizophrenia with pronounced deficits in the somatosensory system.

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Date Created
2019-05

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Corrective Responses to Auditory Feedback Perturbations During Speaking

Description

The brain continuously monitors speech output to detect potential errors between its sensory prediction and its sensory production (Daliri et al., 2020). When the brain encounters an error, it generates a corrective motor response, usually in the opposite direction, to

The brain continuously monitors speech output to detect potential errors between its sensory prediction and its sensory production (Daliri et al., 2020). When the brain encounters an error, it generates a corrective motor response, usually in the opposite direction, to reduce the effect of the error. Previous studies have shown that the type of auditory error received may impact a participant’s corrective response. In this study, we examined whether participants respond differently to categorical or non-categorical errors. We applied two types of perturbation in real-time by shifting the first formant (F1) and second formant (F2) at three different magnitudes. The vowel /ɛ/ was shifted toward the vowel /æ/ in the categorical perturbation condition. In the non-categorical perturbation condition, the vowel /ɛ/ was shifted to a sound outside of the vowel quadrilateral (increasing both F1 and F2). Our results showed that participants responded to the categorical perturbation while they did not respond to the non-categorical perturbation. Additionally, we found that in the categorical perturbation condition, as the magnitude of the perturbation increased, the magnitude of the response increased. Overall, our results suggest that the brain may respond differently to categorical and non-categorical errors, and the brain is highly attuned to errors in speech.

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Date Created
2021-05

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Startle-evoked movement in multi-jointed, two-dimensional reaching tasks

Description

Previous research has shown that a loud acoustic stimulus can trigger an individual's prepared movement plan. This movement response is referred to as a startle-evoked movement (SEM). SEM has been observed in the stroke survivor population where results have shown

Previous research has shown that a loud acoustic stimulus can trigger an individual's prepared movement plan. This movement response is referred to as a startle-evoked movement (SEM). SEM has been observed in the stroke survivor population where results have shown that SEM enhances single joint movements that are usually performed with difficulty. While the presence of SEM in the stroke survivor population advances scientific understanding of movement capabilities following a stroke, published studies using the SEM phenomenon only examined one joint. The ability of SEM to generate multi-jointed movements is understudied and consequently limits SEM as a potential therapy tool. In order to apply SEM as a therapy tool however, the biomechanics of the arm in multi-jointed movement planning and execution must be better understood. Thus, the objective of our study was to evaluate if SEM could elicit multi-joint reaching movements that were accurate in an unrestrained, two-dimensional workspace. Data was collected from ten subjects with no previous neck, arm, or brain injury. Each subject performed a reaching task to five Targets that were equally spaced in a semi-circle to create a two-dimensional workspace. The subject reached to each Target following a sequence of two non-startling acoustic stimuli cues: "Get Ready" and "Go". A loud acoustic stimuli was randomly substituted for the "Go" cue. We hypothesized that SEM is accessible and accurate for unrestricted multi-jointed reaching tasks in a functional workspace and is therefore independent of movement direction. Our results found that SEM is possible in all five Target directions. The probability of evoking SEM and the movement kinematics (i.e. total movement time, linear deviation, average velocity) to each Target are not statistically different. Thus, we conclude that SEM is possible in a functional workspace and is not dependent on where arm stability is maximized. Moreover, coordinated preparation and storage of a multi-jointed movement is indeed possible.

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Date Created
2016-12