Reading and the brain - week 3 (Nicholas) Flashcards
(13 cards)
The ‘visual word form‘ area (Cohen et al. 2000)
Left ventral occipito-temporal cortex.
‘Brain letter box’, or gate to the reading system.
Activated specifically by letter strings acceptable in the language (e.g. NGTH but not TGNH, in English), as well as by existing words (see Glezer et al., 2015).
Cohen et al., 2000
Stage 1: Processing restricted to the contralateral hemisphere (Visual area 4, occipital pole).
Stage 2: Transfer of information from both occipital poles to a more ventral region of the left occipital lobe (Visual word form area).
-Because the visual word form area is located in the left hemisphere, information coded in the primary visual areas in the right hemisphere (i.e., the left visual hemi-field) has to cross to the left hemisphere. This transfer from right to left is done via the corpus callosum, which connects the two hemispheres.
-In contrast, the information already coded in the left hemisphere (i.e.., the right visual hemi-field) does not have to cross. It is sent within the same hemisphere instead.
Lesions
In case of a lesion at an early age, the visual word form area can swap to the right hemisphere.
-This is a case where the highly plastic nature of the brain early on has allowed development of the visual word form area the right hemisphere, as the corresponding region in the left hemisphere was not there anymore.
Marinkovic et al. (2003)
Looked at the timecourse of visual word processing, using magneto-encephalography (MEG).
Estimated the peaks of cortical activity and its progression over time.
During reading, activation starts in both occipital poles.
At about 170ms it shifts to the left occipito-temporal region.
At about 230ms activity explodes in regions of both temporal lobes.
From 300ms onwards it extends over prefrontal and other temporal regions especially in the left hemisphere, before falling back in part to the posterior visual areas (occipital pole).
Catani et al., 2003
-Fibres depicted in red convey information from port-to-port, in an omnibus fashion; those depicted in green work like motorways.
-In the reading system, obviously, these two types of fibres are especially important in the left hemisphere, to transfer information from the ventro-occipital regions (VWFA) to both posterior areas of the frontal lobe and temporal regions.
‘repetition suppression’
stimulus repetition leads to a reduced neural response.
What does the VWFA exactly code?
Glezer et al. (2015)
If the VWFA only codes knowledge about familiar letter strings (‘ght’ vs. ‘htg’), then the more S2 is similar to S1, the weaker the neural response:
vight-vight (S) < pight-vight (1L) < falm-vight (D)
-However, if the VWFA contains neuron populations each coding a familiar word, then repetition suppression should be abolished by just changing one letter between two real words.
right-right (S) < light-right (1L) = calm-right (D)
-This is exactly what they found!
-Pseudoword pairs showed a graded effect, whereas real words and trained pseudowords showed all-or-none repetition suppression!
Cognitive models
Cognitive models make predictions about the functional overlap between brain regions involved in reading.
Thus, brain regions sensitive to these contrasts should correspond to the model’s components (e.g., input lexicon, grapheme-to-phoneme transcoding, etc. ).
(Taylor et al. 2012)
-They examined whether 36 neuroimaging studies of reading pointed at the same brain regions regarding two main contrasting dimensions in DRC:
lexical status (i.e., words vs. nonwords; Is the stimulus part of your long-term memory?)
regularity (i.e., regular/irregular; Can the word be read correctly by both routes?)
-They distinguished between engagement vs. effort in how these dimensions translate into BOLD (Blood Oxygen Level Dependent) signal (i.e., amount of oxygen needed by a region).
-Engagement refers to whether or not the brain region in question is able to deal with the stimulus. In other words, it refers to the capacity of the stimulus to evoke knowledge in that region.
-Effort refers to the amount of resources/fuel required to code and process the stimulus in that region, once the region is engaged.
-But first, they tested whether the distinction between engagement and effort made sense in DRC
-Check their relevance by looking at the activity in the input lexicon (in the computerized version).
Confirms that the distinction between engagement and effort is a valid one!
Lexico-semantic pathway
engagement: words minus peudowords
effort: low-frequency minus high-frequency words
Input lexicon
engagement: irregular words minus non-orthographic strings
effort: (low-F) irregular words minus (high-F) regular words
Print-to-sound conversion/phoneme output buffer
engagement:
-pseudowords minus non-orthographic strings
-irregular words minus non-orthographic strings
effort:
-pseudowords minus regular words
-irregular words minus regular words
Subtraction logic
- In order to isolate the regions specifically involved in recognizing existing words, one should take the brain activity elicited by word stimuli and subtract from it the activity elicited by unknown words.
- This removes the activity common to processing the two kinds of stimuli from the brain map generated by existing words. Hence, this identifies the neural activity specific to lexical processing (i.e., the lexical route).
