Lecture 10- Reading and object recognition Flashcards
How long has written language existed for and what does that mean?
-6000 years -that means the brain system encoding it has also existed only this long -it appeared suddenly and relatively mature -no time for evolution of a reading brain -where did our ability to read spring from?
What is visual invariance?
-we recognise written words over a wide range of size, font or case -we are sensitive to th emost minor changes that affect meaning -reading as a skill does not depend on what we are reading, doesn’t matter what size, font -somehow the info you get out from it is independent from the form to quite a big extend
Do you see eight and EIGHT as the same word?
-yes, despite not having any letters in common -but sight and eight as different eventhough they share almost all of the letters
How are words analysed?
-the brain analyses words by breaking it down into letters, syllables, morphemes, word
What are morphemes?
-the smallest units that carry some meaning (un-button-ing) -button is made up of two syllables (bu and ton) -syllables are made up of graphemes/ phonemes (written letters/sounds of letters)
What are the two routes to understanding a word?
-phonological -lexical -these two approaches work in parallel
How are the levels of the word considered in the brain (syllables, letters, morphemes)?
-each of these is considered almost simultaneously -result feeds two different ways of assigning meaning to the word (phonological and lexical)
What is the phonological route to understanding words based on?
-pronunciation of the word -say the word internally to activate the audible language system to recover meaning
What is the lexical route to understanding words based on?
-goes straight to meaning by comparing whole word to internal dictionary -uses shape recognition
When will you use lexical route?
for common words, irregular words( the ones which are not easy to sound out as they are irregular
When will you use the phonological route?
-regular or uncommon words
Which types of words cause confusion with which type of route to use?
-homophone: use lexical as they sound the same -words with very irregular spelling “enough” is “inog” phonologically= so lexical better
What do brain lesions show about the phonological and lexical routes?
-brain lesion can affect one and not the other route -e.g. deep dyslexics can’t pronounce sextant or made up words like departition, lose the phonological route -other patients have to slowly sound out a word to allow access to its meaning -this means that there are 2 sets of individual neural circuits for each
How does understanding of words (written) work in a healthy person?
-normal people have both routes at work and they work at the same time, the one getting the answer first will tell you
What is the process of identifying a word?
-massively parallel (lot of things happening at once) -competitive, one that gives you answer the fastest wins -robust (fonts, size etc. do not matter) -each aspect of a word gives a clue -all parts get a vote for a guess at word identity
How does the voting for a word work?
-each level is encoded by a group of neurons -each group is looking at a different aspect of the written word (put in a vote for their letter morpheme or word) -also top down votes (you see what you expect) -each hierarchy level is interested in different aspects -down= aspects of letters) -middle= the letter -upper laayer= bits of brain looking for the individual word the upper bits talk to the bottom levels, backwards and forwards system at which of the possible words are you seeing
What are the consequences of the model (voting for words)?
-recognition time is invariant up to around 6-7 letters (then slows down) -ambiguities in letters resolved by rest of word (the e replaces by c, if consistent you read it as e) -can identify a letter flashed onto a screen than a letter alone -comparing d and t need less time in words heat and head -word recognition time correlates with number of similar words in lexicon (hare takes a longer time because you must distinguish from bare, care, dare, here etc) but idea with no similar words is fast
Can you lose the ability to read without losing speech and writing?
-yes, indicates that different parts of the brain are responsible -some people lose ability to identify letters in any form, some retain ability to identify letters but lose ability to process letters in parallel, read slowly by sounding out the letters -alexia= inability to read
What is the pattern of brain activation in reading?
-50ms later after the left or right visual field= then goes into the left occito-temporal sulcus!! -always LEFT -where does it go from there? -after occipital lobe moves to the inferior temporal lobe up to parietal and temporal and then distributed through the brain -after occipital lobe, goes into language circuits
What is the primary area involved in reading?
-ventral occipito temporal cortex -many names for this -inferior surface temporal lobe -visual word-form area (VWFA)= he doesn’t like it -all readers use this area irrespective of the language they were taught to read -always activated by reading tasks in any form (also can be called inferior or ventral temporal lobe)
What is the first are activated in reading tasks after V1?
-LEFT ventral occipito-temporal cortex -doesn’t matter in which visual field the stimulus is -tested by: using magnetoencephalography (nearly instantaneous but low resolution) -after being shown words occipital lobe activated at 100ms (V1) at 200ms the words activate the left ventral occipito-temporal cortex
What is the pattern of brain activation in reading?
-50ms later after the left or right visual field= then goes into the left occito temporal sulcus!! -always LEFT -where does it go from there? -after occipital lobe moves to the inferior temporal lobe up to parietal and temporal and then distributed through the brain -after occipital lobe, goes into language circuits
What activates after the inferior occipito-temporal cortex in reading?
-magnetoencephalography reveals the progressive activation of language circuits by written words -activation spreads from occipital lobe through ventral-occipital temporal cortex into classical perisylvian language areas -by 420ms making lexical and semantic identifications -signal in inferior temporal lobe, after 250ms to language cicruits
What are the questions about origin of the reading network?
-doesn’t explain where the reading network comes from -why is letter box in the left inferior occipito-temporal cortex -how did we evolve the system in six thousand years -connected to object recognition
