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PSYB65H3 (479)
Ted Petit (185)
Chapter 4

Chapter 4 psyb65

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University of Toronto Scarborough
Ted Petit

06/12/12 Chapter 4 -laterality: functional specialization of the right and left hemispheres -Left Hemisphere (LH)-> language and right body control -Right Hemisphere (RH)-> music, emotion, spatial abilities, left body control -RH capabilities took longer to understand-> damage resulted in subtle differences compared to LH -although methods expressed is in separate LH and RH methods, the two often intermingle and are in constant communication eg) sarcastically said: ‘nice shoes’; LH interprets the words, RH interprets the tone ->prosody: sound waves that compose emotional tone of speech Methods -Split Brain -RH + LH communicate with commissural systems -> anterior + posterior commissures, corpus collosum, habenular commissure, hippocampal commissure -when the corpus collosum is severed, communication b/w LH and RH is severed -largest in the commissural system ->originally cut to help stop epilepsy -when it continued, the cut the remaining commissural system, stopping the seizures -with the two separated, RH does not deal with writing, was incapable of arranging letters -RH capable of recognizing faces -Intracarotid Amobarbital Testing -IAT: used to asses laterality of language in people to be undergoing brain surgery ->sodium amobarbital (anaesthetic) is injected into the carotid artery eg) injection into the right carotid artery results in right side of the brain ‘sleeping’ ->then cognitive function is analysed-> language, memory -IAT is an invasive procedure ->preferable to determine which hemisphere is responsible for speech sounds -Visual System -sends information from retina receptors to both hemispheres -Left visual field (LVF) is transmitted to primary visual cortex of RH from the nasal hemiretina of the left eye (closest to the nose) + temporal hemiretina of the right eye(closest to the temples) ->vice versa for RVF ->communicated via corpus collosum -the division of sight occurs in the periphery of the retina -tests of visual functions occur in one’s peripheral-> so fovea cannot observe eg) patient to stare at a stimulus that is more than 1degree from the centre + stimulus presented briefly-> no chance for eyes to adjust to the centre of the screen -Auditory System -not as segregated as visual system-> cochlea receptors project bilaterally -ipsilateral hemispheres are weaker, less numerous + slower when segregated than contralateral projections eg) when not segregated and stimuli presented in ears simultaneously, RH prefers to attend to the left ear, and vice versa -Dichotic Listening -takes advantage of ipsilateral projection suppressions during competing stimuli -different stimuli presented per ear and patient is asked to focus in on one certain stimuli and answer if present or not eg) the word ‘cat’ ->preferable in perception of speech sounds ->correct responses per ear are tallied -most often, patients get correct results in the right ear more than the left during words/phonemes as stimuli -most often, patients get correct result in the left ear more than the right during music/environmental sounds as stimuli -Tachistoscopic Presentations -advantage of segregation in the visual system -rapid stimulation to RVF or LVF using a tachistoscope (allows rapid presentation of stimuli) -patient then asked to report what they saw + correct responses per visual field is tallied ->using words/letters/linguistics as stimuli= LH favour (RVF) ->language, facial recognition, emotionless expressions, spatial location judgement as stimuli= RH favour (LVF) -similar to dichotic listening Neuroanatomical, Neurochemical and Behavioural Findings -human brain appears physically + functionally asymmetric -false; right frontal lobe protrudes farther; left occipital lobe extend more behind -Neuroanatomical Asymmetries -general anatomical trends -rate of maturation-> gyri + sulci develop earlier in the LH -size of complete hemispheres-> RH is larger + heavier than LH (not every part, but in sum) -ratio of grey to white matter-> gray/white matter ratio higher in LH (more gray matter) -density of neural tissue-> b/c of gray/white matter ratio, LA exhibits greater cell packing density -asymmetries in specific structures within the hemispheres -sylvian fissure extends more horizontally in LH, and ascends higher in RH ->evidence shows as early as 60,000 emergence -planum temporal-> region under temporal love under posterior tip of sylvian fissure -often longer planum temporal in LH (up to 10x larger) -usually one Heschl’s gyrus in LH, but two in RH -connections b/w the two halves of the brain -corpus collosum -homotopic + heterotopic connections ->splenium, body of corpus collosum + genu -rostrum: inferior to the body and at the end of the genu bend -massa intermedia: connects the two thalami -hippocampal commissure: connects the two hippocampi -anterior commissure + posterior commissure -Neurochemical Asymmetries -> refer to Table 4.6 (p.114) -Functional Asymmetries -verbal/nonverbal -claiming all linguistic problems are associated with LH ->similarly claiming all nonverbal manner problems= RH -LH domination is not strictly dependant on linguistic issues-> can also be non-linguistic -local/global processing -stimuli where the local elements do not correspond with the global elements eg) using F’s (local elements) to make up the shape of an H (global element) -most people take into account the global element before the local element (longer reaction time to identify the local element) ->local processing + global processing function under anatomically + functionally distinct systems -LH damage impairs local element identification -RH damage impairs global element identification -high spatial frequency/low spatial frequency -spatial frequency hypothesis: 2 hemispheres differ in their ability to process basic sensory attributes of various stimuli ->difference is the detail, attunement; squinting your eyes at an object, versus wide open -LH is more sensitive to high spatial frequency; RH is more sensitive to low spatial frequency ->these emerge at a later stage of cognitive processing -to define local/global elements, it must be defined by spatial frequency eg) think of it like ‘the big picture’-> global elements/low frequency (RH) ‘smaller picture’->local elements/high frequency (LH) -high temporal frequency/low temporal frequency -similar to preceding section, but with ability to process stimuli presented rapidly -LH/RVF processes rapid events faster -lights being flashed fast enough isn’t recognized as a flash eg) watching a movie at a theatre ->ability to detect rapid flashes are not equal per hemisphere (higher for LH) Why is there Hemispheric Specialization? -Environmental/Psychosocial Theories -Jackson’s parental pressure theory -handedness is determined entirely by the child’s environment ->child is right handed because parents were, vice versa-> any child can be right handed/left handed/ ambidextrous -Blau’s psychodynamic theory -handedness was a result of environmental circumstances as well ->emotional negativism-> no biological basis -Problems with environmental/psychosocial theories -handedness runs in families regardless of child’s parent’s handedness eg) adoption cases showed handedness closer to biological parents -left handedness has occurred over centuries-> when it was once bad -why would it persist? -siblings (including identical twins) do not always have the same handedness despite similar/identical environments -newborn fetus exhibits its own asymmetries before environmental influences take place -Genetic Theories
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