SPEECH PERCEPTION The Speech Stimulus Perceiving Phonemes Top-Down Processing Is Speech Special?
The Speech Stimulus Spoken words are composed of phonemes phoneme: smallest unit of speech that affects the meaning of a word
The Speech Stimulus: Articulation vocal tract open or closed: vowels are produced with the vocal tract open voicing: vibrating of vocal cords place of articulation: point at which airstream is blocked manner of articulation: degree to which airstream is blocked
Analyzing The Speech Stimulus sound spectrogram - graph showing intensities of various frequencies over time formants - bands of high intensity frequencies in vowel sounds formant transitions - shifts preceding or following formants; carry information about consonants
Perceiving Phonemes variability problem: acoustic properties of phonemes change depending on – context (coarticulation) – speech rate – speaker – loudness
Perceiving Phonemes segmentation problem: there is often no clear separation between one phoneme and another
Perceiving Phonemes categorical perception: phonemes are perceived as categories; many different sounds can be perceived as within the same phonemic category
Top-Down Processing of Speech phonemic restoration effect: listeners perceive a phoneme even when it is deleted and replaced by noise demonstrates effect of context on speech perception
Top-Down Processing of Speech McGurk Effect: phoneme perception is affected by visual cues about lip movements demonstrates effect of visual information on speech perception
Top-Down Processing of Speech The problems for speech perception are general perceptual problems, such as constancy Similar top-down processing strategies might be used (e.g., Gestalt heuristics)
Top-Down Processing of Speech indexical characteristics - characteristics of a person’s voice that carry information about – Age – Gender – Emotion – Region – Intent
Is Speech Special? According to the “Speech is Special” hypothesis, we have a speech module: specialized abilities for perceiving speech Motor theory: the speech module contains knowledge of how phonemes are produced; we use this knowledge for speech perception
Is Speech Special? Left hemisphere specialized for language – Broca’s area - damage causes Broca’s Aphasia – Wernicke’s area - damage causes Wernicke’s aphasia Categorical perception of phonemes
Is Speech Special? Although locations in the left hemisphere are important for speech, specific brain areas are important for other perceptual abilities as well Categorical perception of phonemes does not require a speech module because: – Infants show categorical perception of phonemes – Quail and chinchillas also show it – Non-speech sounds can be perceived categorically