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
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 gateway to language circuits?
-angular gyrus -all non auditory language symbols seem to converge on this site (e.g. written language, sign language, mathematics) -gateway to information linked to written word (meaning, grammar, emotional content, phonological decoding) -angular= is gateway to symbolic circuits, braille etc, enter via angular gyrus
What do lesions in the ventro-occipito-temporal cortex involve?
-this is the object recognition area -lesions here inhibit object recognition in both humans and moneky -lesions: what do they show us: -small localised lesions can the individual can no longer recognise objects -ventral parts of the temporal lobe= the lesions
What is the organisation of recognition modules?
-micro map surface of ventral occipito temporal cortey for response of single neurons to simplified visual stimuli -each shape represented by multiple cells -form columns around 400 um wide, extend through full thickness of cortex -neighbouring columns each respond to slightly different versions of same shape -form hypercolimn concerned with single type of object -there are columns that respond to similar things -hypercolumns= columns of cells, interested in similar things
How did they achieve visualisation of hypercolumns?
-can visualize whole column response by changes in blood flow to surface of cortex -stimuli: different views of the same object -columns responding to different views of same object (hypercolumns) overlap -multiple views of same object brought together in one area and treated as equivalent for identification? -hypercolmun provides invariant view -we are looking at single cells. -but brain works in columns -patch of cortex lit up as more blood in here -they are connected, overlap, the hypercolumns
