Chapter 6: Motor Theory of Speech Perception – Flashcards
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when a stop consonant is produced in various vowel consonant contexts there is no apparent consistent acoustic cue that can account for its constant perception
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acoustic invariance
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since there must be invariant or constant motor commands to the articulators to produce the same consonant in different vowel contexts, the ___ ___ could exploit these motor commands
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perceptual process
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neural messages that the brain sends to set the articulators in motion to produce speech
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motor commands
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researchers theory: though we cannot exclude the possibility that a purely ___ ___ exists, we find it more plausible to assume that speech is perceived by processes that are also involved in its production
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auditory decoder
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___ ___ offers important cues about speech perception which can be used by listeners (weak version of motor theory), and quite another to state that it forms the basis for speech perception (stronger version of motor theory)
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speech production
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one problem with the theory is that it has never been made explicit just how listeners would ____ motor commands from the acoustic signal
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extract - not all clear how a person could make the link between acoustic speech signals in the air & motor commands in a speaker's brain that would have produced such signals
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major drawback of motor theory is that once the problem of how listeners perform the link between the acoustic signal & motor commands is solved, why would listeners not simply go directly to ___?
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phonemes - link from acoustic signal to phonemes seems somewhat more direct than in intervening link between acoustic signal & motor commands in speech articulators
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just how the motor commands are linked up with the acoustic signal remains an important problem, presuming listeners are what?
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not capable of having access to motor commands from a speaker other than via the acoustic signal - as listeners we don't have modem that physically link us up with the motor commands in a speaker's brain (takes this point to the extreme)
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one means of investigating the motor theory was to look directly at the neural signals to the muscles of articulation via _____?
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electromyography (EMG)
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what happens in electromyography?
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- electrodes are either placed on the surface of the skin directly about muscles or, for even more accurate recordings, directly into muscles - electrodes then record directly the electrical impulses that trigger muscle contractions
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in the early studies of EMGs what happened?
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traces appeared to be just as variable as the acoustic signal - certainly did not support a strict interpretation of motor theory
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another piece of evidence that seems to go against the motor theory is the fact that patients with ___ __ (damage to speech center of brain) who have serious motor problems in producing speech don't seem to have a significant problem with speech perception
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broca's aphasia - speech perception doesn't seem to be on a tight link between production and perception
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patients with ___ __ (resulting from lesion in another portion of brain) who don't usually experience motor speech problems typically seem to have difficulties with speech perception than those with broca's aphasia
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wernicke's aphasia - speech perception abilities of these types of aphasics have not been shows to be statistically inferior to broca's aphasics
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what are some evidence for motor theory?
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- foreigner's that read lips to attempt to understand - profound hearing loss can lip read from peoples lips and faces - McGurk Effect
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what is the McGurk effect?
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listeners combine visual info on speech production with auditory info - listeners make an agglomeration of the auditory & visual modalities & perceive a place of artic that is intermediate between the 2 delivered by seeing & listening (ex: TV ads when an animal's lips move & sync with a talking voice)
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the weaker version of motor theory which still captures the influence of production in perception is in order because in a weakened version...
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speech perception would not be driven by (or entirely based on) motor commands
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the revised version of the motor theory does what?
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attempts to take into consideration new information gathered since the original theory was first developed
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what are the 2 new developments that the newer version of the theory seeks to take into account?
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- concept of modalities - duplex perception
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what is a modality?
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specialized subprocessing routines in the brain - this idea for the basis of modules is that the brain has developed specialized areas fro treating certain perceptual info (areas act somewhat independently of other brain processing)
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what is the duplex perception?
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transitions for F1 are presented to one ear, while those for F2 are presented to the other ear - what some listeners hear is both speech & non speech at the same time so the same acoustic info can be simultaneously processed in both speech and non speech modes
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the duplex perception created a specialized perceptual mode for treating speech has evolved in human beings which is...
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one that exploits the invariant relationship between motor gestures & the acoustic signal in order to decode speech
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because of the concept of modalities and the duplex perception what is the revised motor theory state?
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phonetic info is perceived in a biologically distinct system, a module specialized to detect the intended gestures of the speaker that are the basis for phonetic categories
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what is the analysis-by-synthesis theory?
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perception is somewhat based on production and listeners are hypothesized to decode the acoustic signal by internally generating matching signals - the signal that provides the best match is the one perceived by the listeners
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what is the difference between the motor theory and the analysis-by-synthesis theory?
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the analysis-by-synthesis theory does not stipulate that it is specifically motor commands that mediate perception - analysis-by-synthesis also requires a matching process with the acoustic signal
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what is one account for the means by which the matching process between the acoustic signal & phonemes occur in analysis-by-synthesis? (borrowed from study of visual perception)
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the concept of internalized recognition patters, or templates, has proven to be a powerful metaphor for explaining visual perception
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a similar problem to the matching by visualization in the original proponents of analysis-by-synthesis is what?
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the manner by which they proposed to circumvent this problem was to perform a "pre-analysis" in which the speech signal was broken down into distinctive features
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Did early EMG studies attempt to support or contradict motor theory?
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contradict
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what is a drawback to using a stencil-mathcing procedure to discover which letter was produced?
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time consuming
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the motor theory was brought about to solve?
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acoustic invariance
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what is the weak version of motor theory
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speech production offers important cues about speech perception
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what is the strong version of motor theory
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speech production is the basis for speech perception
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name 3 pieces of evidence against the motor theory
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- never been made explicit how listeners would extract motor commands from acoustic signal - EMG would not be able to pick up muscle activities (just as variable as acoustic signal) - patients with broca's aphasia do not have a problem w/ perception but have serious motor problems
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name 3 piece of evidence for the motor theory
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- speech reading in the hearing impaired - mcgurk effect - visual info influences speech perception (foreigners using lips to understand)
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in analysis-by-synthesis, listeners are hypothesized to decode the acoustic signal by internally generating ___ ___
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matching signals
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what is the main drawback to the analysis-by-synthesis theory?
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its a lengthy process to discover which letter was printed (internalized recognition patterns or templates)
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how can we circumvent the drawback of the analysis-by-synthesis theory?
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to perform a "pre analysis" in which the speech signal is broken down into distinctive features
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T/F in duplex perception tasks, we will typically expect to see results showing a right-ear advantage
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F
