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Cognitive Neuroscience Chapter 11

Terms in this set (42)

Semantic Paraphasias
- The production of a word related in meaning to the intended word (e.g. horse for cow) instead of the intended word itself. Wernicke's aphasia patients often produce semantic paraphasias.
- Errors in speech production common in patients with Wernicke's aphasia. (saying horse when they mean cow). Also deep dyslexic patients might read Horse when Cow is written. These errors support the semantic network idea of the mental lexicon in that related meanings are substituted, confused, or lumped together.
Mental Lexicon
A mental state of information about words that includes: semantic information or word meaning, syntactic information or how words combine to form sentences and word forms or how they are spelled and their sound pattern. It has an enormous capacity, a relatively fast retrieval of information, information content changes, and must be efficiently organized. It is often conceptualized as a network, with words that are more closely related in closer proximity on the network (supported by semantic priming studies).
- A mental store of information about words, including semantic information (meanings of words), syntactic information (rules for using the words), and the details of word forms (spellings and sound patterns). A store or stores of information about words exist in the brain.
Semantic Information
- Word meaning
- Representations in the mental lexicon are organized according to meaningful relationships between words. Words related in meaning must somehow be organized together in the brain, such that activation of the representation of one word also activates words that are related in meaning. This makes words easier to recognize when they follow a related word that primes their meaning.
- The way that meaning is represented in the words of language.
Syntactic Information
- How words combine to form sentences
- The rules that constrain word combinations and sequences in sentences.
Word Forms
- How words are spelled and their sound pattern. Morphemes are the smallest meaningful unit in language (frost 1 - defrost 2 - defroster 3). Some words also differ from any single word by only one phoneme or one letter.
Phoneme
The smallest unit of sound that makes a difference to meaning. Ex: In English, L and R in the words late and rate. Words with many overlapping phonemes or letters must be organized together in the brain, such that when incoming words access one word representation, others are also initially accessed, and selection among candidate words must occur, which takes time.
- The smallest perceived units of sound in a language, of which, for example, there are 40 in the English language.
Lexical Decision Task
Lexical selection is the process of selecting from a collection of representations the activated word that best matches the sensory input.
- Subjects are presented with pairs such as
Nurse-Doctor
Nurse - Todcor
Butter- Doctor
Butter - Todcor
In semantic priming studies that use the lexical decision task, participants are presented with pairs of words. The first member of the word pair of the prime is a real word, the second member of the pair is called the target and it can be either a real word or a psuedoword. If the target is a real word it can be related or unrelated to the prime. For the task, the participant must decide as quickly and accurately as possible whether the target is a word, by pressing a button. Participants are faster and more accurate at making the lexical decision when the target is preceded by a related prime, than an unrelated prime. Words related in meaning must somehow be organized together in the brain, such that activation of the representation of one word also activates words that are related in meaning, making it easier to recognize them when they follow a related word.
Collins & Loftus (1975) model of the metal lexicon
They proposed a model to explain the effects of semantic priming during word recognition. In it word meanings are represented in a semantic network in which words, represented by conceptual nodes, are connected with each other. The strength of the connection and the distance between the nodes are determined by the semantic relations or associative relations between the words. (ex car will have a close and strong connection with truck). It assumes that activation spreads from one conceptual node to others, and nodes that are closer together will benefit more from this spreading activation than will distant nodes.
-Words that have strong associative or semantic relations are closer together in the network (car and truck) than are words that have no such relation (car and clouds). Semantically related words are colored similarly in the figure and associatively related words (firetruck-fire) are closely connected.
Wernicke's Aphasia
- A language deficit usually cause by brain lesions in the posterior parts of the left hemisphere. resulting in comprehension deficits.
- A disorder of language comprehension. Patient's can produce fluid sounding speech but it is meaningless. Dense and persistent Wernicke's aphasia only results when Wernicke's area is damaged AND the surrounding cortex of the posterior lobe is damaged OR there is damage to the underlying white matter that connects the temporal lobe language areas to the other brain regions.
- Damage to the posterior regions of the superior temporal gyrus (wernicke's Area). Damage to wernicke's area does not actually cause the syndrome, instead, secondary damage due to tissue swelling, in the surrounding regions contributes to the most sever problems, when swelling around the lesioned cortex goes away, comprehension improves.
Neurological Evidence Supporting the Semantic Organization of the Brain
Warrington and his colleagues did research that said semantic problems can be localized to specific semantic categories. Ex. patients who have difficulty naming living things but can name man-made things VS patients who can name living things, but they can't name man-made things. These deficits suggest an organization of semantic information in the brain.
PET and fMRI studies have shown that dmage to the left temporal pole (TP) correlates with problems naming persons. Damage to the anterior of the left inferior temporal lobe (IT) correlates with problems in naming animals. Damage along the lateral temporo-occipito-parietal junction (IT+) correlates with problems in retrieving the names of objects.
Figure 10.3
Brain areas important to speech perception and language comprehesion - Acoustic sensitivity decreases moving anteriorly and posteriorly away from primary auditory cortex, while speech sensitivity increases. Anterior and posterior regions of the superior temporal sulcus are increasingly speech specific. Posterior inferior temporal lobe and prefrontal regions are also important during speech processing. Heschl's gyrus (primary auditory cortex; red spot) is not speech specific, but is instead activated by all auditory inputs.
Figure 10.4
Speech Waveform for the question "What do you mean?" - Note that the words do you mean are not physically separated. Even though the physical signal provides few cues to where the spoken words begin and end, the language system is able to parse them into the individual words for comprehension.
Lexical Selection
The process of selecting from a collection of representations the activated word that best matches the sensory input.
- Lexical representation in the mental lexicon that best matches the input cane be identified (selected). It comes after lexical access (output of perceptual analysis activates word-form representations in the mental lexicon, including their semantic and syntactic attributes), and before lexical integration ( integrates words into the full sentence, discourse, or larger context).
Problems associated with spoken input in language
Spoken input is where the listener must identify sounds from noise usually done through distinguishing phonemes (smallest unit of sound) in order to distinguish differences in meaning. Problems may include variability in the signal, such as phonemes differing depending on what sound follows them (Ex. bo and bi are different, bi and di are similar), or factors like an accent, a male VS female voice, and how loud or soft the input is. Also the same speech sound produced by different speakers can cause problems in understanding. Word boundaries are murky in spoken language, but are very clear in written language as phonemes do not appear as separate little chunks. Also segmentation problems that make the boundaries within and between words unclear, and lastly prosodic information such as raising frequency when asking a question at the end, or raising loudness or pausing between words for emphasis.
Figure 10.7
Lateral view of the left hemisphere language areas and dorsal connections - Wernicke's area is shown shaded in red. The arcuate fasciculus is the bundle of axons that connects Wernicke's and Broca's areas. It origniates in Wernicke's area, goes through the angular gyrus, and terminates on neurons in Broca's area.
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