Psycholinguistics/Neural Basis of Speech Perception/Learning Exercises Answers
The Neural Basis of Speech Perception
Examples of potential responses to the learning exercises on the neural basis of speech perception.
Using a passive listening task to speech, the study may not have controlled for temporal differences in the speech stimuli. The right auditory cortex is less sensitive to temporal cues, only responding to slow speech stimuli. The left auditory cortex is highly selective for fast changing temporal information that is characteristic of speech signals. If the study was only examining early speech perception, and chose to use a fast speech signal, it may have shifted this activation to predominately the left hemisphere. Conversely, if they slowed it down it may have caused activation to favour the right hemisphere. It is has been shown that there are bilateral, but asymmetrical differences in phonological processing.
The ventral stream maps phonological information onto semantic representations. It is organized bilaterally, but asymmetrically. The Dorsal stream translates speech signals into articulatory representations in the frontal lobe.
Moment-to-moment shifts in goals or strategies, phonological rehearsal and analysis, all require the active manipulation of words, or thoughts. Therefore, the researchers appear to be discussing under the same umbrella term of executive functions that are commonly classed as a function of the lateral prefrontal cortex. In terms of Broca’s area precise function, it appears more likely to be involved in multiple aspects of utilizing language.
The two processing streams have a common area bilaterally organized in the superior temporal gyrus. This is the location where the primary auditory cortex resides, and is attributed to early stages of speech perception. Activations are attributable to preliminary speech and auditory processing, differentiating the auditory stimuli into the perception of speech or sounds in general. Therefore, this would also be the location that musical sounds would be initially analyzed.
The researchers are investigating the same topics, but use very different measures to evaluate them. It is difficult to compare activations observed in a PET study, against one in an fMRI study, as they are not attempting to replicate the same results. Although different methods can provide additional support, in this case they use different tasks. The word listening and repetition task is going to elicit wider brain activations for listening to, and producing speech. The semantic decision task will give a better idea of the areas that are associated with semantic decision-making that can be compared against the nouns that did not require a button press.
The temporal lobe is involved in language processing, including the processing of auditory sounds, phonemes, syllabic/phonological structures, grammatical, and semantic information.
The superior temporal gyrus is where the primary auditory cortex resides, and is the initial point of sound processing. Phonological processing of syllables and phonemes also takes place here.
The middle temporal gyrus is involved lexical and semantic information processing, in other words, linking the phonological representations with the mental lexicon.
Opercular part, Triangular part, Orbital part; known as Broca‘s area. The inferior frontal gyrus was shown active in response to phonological judgment, word retrieval, and semantic judgment tasks. These tasks all require auditory-verbal short-term memory during perception and/or repetition, and therefore caused researchers to attribute Broca’s area activations to phonological rehearsal.
Angular and supramarginal gyri
The ATL would be an appropriate candidate because it is neuroanatomically proximal to the orbito-frontal cortex implicated with an executive function in the linguistic literature, as well as the medial temporal lobe, which is almost always active in semantic decision-making tasks for semantic processing. Further, it is proximal to limbic structures, which influence the affective response in the way we perceive, and the things we know.