Reading & the Brain Flashcards
COHEN ET AL. (2000): ‘VISUAL WORD FORM’ AREA
- left ventral occipito-temporal cortex
- “brain letter box”/gate to reading system
- activated specifically by letter strings acceptable in language (ie. NGTH but not TGNH in English) & via existing words (Glezer et al. (2015))
- area proximity to other regions coding faces/objects supports idea that brain has evolved to perceive letters/words as complex objects
WHY IS THE RIGHT VISUAL FIELD CODED BY THE LEFT HEMISPHERE (VICE VERSA)?
- inner retinas send info across to opposite hemispheres; outer retinas send info to hemispheres on same side
- aka. what is presented in right hemi-field -> left hemisphere (vice versa); NOT projection
- relates to before info in right occipital pole crosses via corpus callosum to reach brain letter box/visual form area (normally developing in left hemisphere)
COHEN ET AL. (2000): VISUAL STAGES
S1) Processing restricted to contralateral hemisphere (V4; occipital pole)
S2) Info transfer from both occipital poles -> ^ ventral region of left occipital love (visual word form area) via corpus callosum (hemisphere bridge) from right -> left; goes straight there if left
COHEN ET AL. (2004)
- kids’ reading networks = more flexible > adults
- early age lesion -> visual word form area can swap to right hemisphere
- highly plastic brain nature early on allowed development of visual word form area in the right hemisphere (as corresponding left hemisphere region is not there anymore)
MARINKOVIC ET AL. (2003)
- looked at time-course of visual word processing using magneto-encephalography (MEG)
- estimated peaks of cortical activity & progression over time
- reading = activation starts in both occipital poles
- 170ms = shifts to left occipito-temporal region
- 230ms = activity explodes in both temporal lobe regions
- 300ms = extends over prefrontal/other temporal regions esp. in left hemisphere before falling back in part to posterior visual areas (occipital pole)
CATANI ET AL. (2003)
- U fibres (occipito-temporal projection system (OTPS)) = info transport port-to-port; located laterally to ILF; connect adjacent gyri of lateral occipito-temporal cortices to form OTPS
- inferior longitudinal fasciculus (ILF) fibres = work like motorways
- both in right hemisphere
- particularly important in left hemisphere (reading system) to transfer info from ventro-occipital regions (VMFA) -> posterior frontal lobe areas/temporal regions
GLEZER ET AL. (2015): PROCEDURE
VENTRO-OCCIPITAL REGIONS (VMFA)
- repetition suppression = stimulus repetition leads to reduced neural response
- if VWFA only codes info about familiar letter strings (“ght” (S1) VS “htg” (S2)) -> the more S2 is similar to S1 the weaker the neural response
- ie. vight-vight (S) < pight-vight (1L) < falm-vight (D)
- BUT if VMFA contains neuron populations each coding a familiar word then repetition suppression should be abolished by just changing 1 letter between 2 real words (did find this!)
- ie. right-right (S) < light-right (1L) = calm-right (D)
GLEZER ET AL. (2015): RESULTS
- VMFA contains neuron populations each coding familiar word; repetition suppression = abolished by changing 1 letter between 2 real words
- pseudoword pairs showed graded effect; real words/trained psuedowords showed all-or-none repetition suppression
TAYLOR ET AL. (2012): BACKGROUND
- cognitive models make predictions about functional overlap between brain regions involved in reading
- word > nonword
- irregular > regular
- aka. brain regions sensitive to such contrasts should correspond to model’s components (ie. input lexicon/grapheme-to-phoneme transcoding)
TAYLOR ET AL. (2012): PILOT PROCEDURE
- examined if 36 neuroimaging studies of reading pointed at same brain regions regarding 2 main contrasting DRC dimensions:
1) lexical status (ie. words VS nonwords aka. is stimulus part of LTM?)
2) regularity (ie. regular/irregular aka. can the word be read correctly by both routes?) - both provide 2 contrasts distinguishing between types of acquired dyslexia as cognitive models = partly derived from reading disorder observation
- distinguished between engagement VS effort in how dimensions translate into BOLD (blood oxygen lvl dependent) signal (ie. oxygen amount needed by regions)
TAYLOR ET AL. (2012): PILOT METHODOLOGY
- peaks in BOLD signal do NOT = region “liking” stimulus; instead that it’s having a hard time processing it
- engagement = whether brain region in question can deal w/stimulus; aka. capacity of stimulus to evoke knowledge in said region
- effort = amount of resources/fuel required to code/process region stimulus once region = engaged
TAYLOR ET AL. (2012): PILOT
- first tested if distinction between engagement/effort made sense in DRC
- check relevance by looking at activity in input lexicon (computerised version)
- results obtained by giving computer-implemented version of dual-route model word/nonword list which model had to recognise/reject
- words in input lexicon earn points in proportion to matching stimulus (ie. letters in correct positions); the more they earn points/frequency in language, the more able they are to deplete competitors; word is recognised once its activation lvl = ligher than its competitors by minimum distance
TAYLOR ET AL. (2017): PILOT RESULTS
- confirm engagement/effort distinction = valid
- existing words generate stronger engagement > unknown words (pseudowords)
- longer for low frequency strings to reach same activity lvl > high frequency words
- activity remains longer in that region of system for low > high frequency words; altogether reflects that recognition isn’t easy for low-frequency words
THE SUBTRACTION LOGIC: WORDS > PSEUDOWORDS
- to isolate regions specifically involved in recognising existing words:
1) take brain activity elicited by word stimuli
2) subtract from it the activity elicited by unknown words - aka. this removes activity common to processing 2 stimuli kinds from brain map generated by existing words; this identifies neural activity specific to lexical processing (ie. lexical route)
DRC MODEL: SYSTEMATIC APPROACH I
- lexical pathway engages words BUT not/weakly pseudoword strings
- taxed more by low-frequency words > high-frequency words
- aka. 2 contrasts pointing towards:
1) lexical route = words - pseudowords
2) lexical route = low-frequency words - high-frequency words