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Speech Perception 2 (Perceiving Degraded Speech (The ability to hear…

- - - - Furthermore, the pop-out effect and later improvement also occurred in a group of subjects who read the sentence after hearing the degraded sentence
        
        This means that it isn't listening to the clear sound, but knowing the content of what they were hearing that helped with learning
  - - - We first are trying to understand them based on the overall meaning of what they are saying and not the individual words
        
        Eventually, listening to determine the overall message results in an increased ability to understand individual words, which in turn makes it easier to understand the overall message
        
        Clearly, transforming sound to meaningful speech involves a combination of bottom-up processing, based on the incoming acoustic signal, and top-down processing, based on knowledge of meanings and the nature of speech sounds
- - - - Results from damage to Broca's area, which is located in the left frontal lobe
      - Characterised by slow, laboured, ungrammatical speech
        
        They also have problems forming complete sentences, as well as difficulty understanding some types of sentences
      - People with Broca's aphasia also have difficulty processing connecting words such as "was" and "by"
      - Due to researchers taking into account both the problems in producing and understanding speech related to Broca's area, they concluded that damage to Broca's area in the frontal lobe causes problems in processing the structure of sentences
    - - Patients typically produce speech that is fluent and grammatically correct, but incoherant
      - Wernicke's area is in the left temporal lobe
      - Patients not only produce meaningless speech, but are unable to understand speech and writing
      - In severe cases, patients have a condition called WORD DEAFNESS - in which they cannot recognize words, even though their ability to hear pure tones remains intact
    - - E.G. Patients with damage to their parietal lobe have difficulty discriminating between syllables
        
        Some of these patients can still understand words
  - - - The ventral pathway is responsible for recognizing speech, and it has been proposed that the dorsal pathway may be involved in linking the acoustic signal to the movements used to produce speech
  - - - Manner of articulation describes how the articulators interact while making a speech sound
      - Place of articulation describes the location of articulation
    - - The neural code for phonemes and phonetic features corresponds to population coding
- - - - Hearing a particular speech sound activates motor mechanisms controlling the movement of the articulators, such as the tongue and lips, that are responsible for producing sounds
      - That activation of these motor mechanisms, in turn, activates additional mechanisms that enable us to perceive the sound
      - Thus the theory proposes that activity of motor mechanisms is the first step towards perceiving speech
  - - - These neurons fire both when a monkey carries out an action that produces a sound and when the monkey hears the sound that results from the action
      - Interestingly, the mirror neurons that have been studied in the monkey, have been found in an area roughly equivalent to Broca's area in humans; for this reason, some researchers have proposed a close link between mirror neurons and language
  - - - Researchers concluded that activity in the motor cortex can influence speech perception
  - - - The idea that production and comprehension share processing mechanisms is the finding that the brains response to production and comprehension was coupled
        
        That is, the time course of the neural responses to these two processes was similar. This makes it more likely that production and comprehension share mechanisms, and shows that just as action and motor mechanisms play important roles in visual perception, there is a close link between production and comprehension (or action and perception) for speech perception as well
- - - - The fact that there are often no spaces between words becomes obvious when you listen to someone speaking a foreign language
        
        To someone who is unfamiliar with that language, the words seem to speed by in an unbroken string. However to a speaker of that language, the words seem separated, just as the words of your native language seem separated to you
  - - - Psychologists describe the way sounds follow one another in a language in terms of TRANSITIONAL PROBABILITES
        
        Transitional Probabilities means the chance that one sound will follow another sound
        
        Every language has transitional probabilites for different sounds, and as we learn a language, we not only learn how to say and understand words and sentences, but we also learn about the transitional probabilities in that language
        
        The process of learning about transitional probabilities and about other characteristics of language is called STATISTICAL LEARNING
        
        Research has shown that infants as young as 8 months old are capable of statistical learning
- - - - Anomalous sentences
      - Ungrammatical strings of words
      - Normal grammatical sentences
      - They used a technique called SHADOWING in which they presented these sentences to subjects through earphones and asked them to repeat aloud what they were hearing
        
        The participants reported normal sentences with an ac- curacy of 89 percent, but their accuracy fell to 79 percent for the anomalous sentences and 56 percent for the ungrammati- cal strings.
        The differences among the three types of stimuli became even greater when the listeners heard the stimuli in the presence of a background noise
        
        These results tell us that when words are arranged in a meaningful pattern, we can perceive them more easily. But most people do not realise it is our knowledge of the nature of our language that helps us to fill in difficult to hear sounds and words
        
        Because we mostly encounter meaningful words and grammatically correct sentences, we are continually using our knowledge of what is permissible in our language to help us understand what is being said. This becomes particularly important when listening under less than ideal conditions, such as in a noisy environment or when the speakers voice quality or accent is difficult to understand