Human visual pathway

Issues in the psychology of reading

Do we process letters or map words (=letterstrings)onto visual templates?

Is reading mediated by sound representations?

Reading ≠ Serial letter processing

Mostaccurate

Could words be processed viavisual templates?

What would the visual templates be like?

dog

d o gdOG

DOG

doGDogDog

dog

d o gdOg

Rayner &Pollatsek: parallelletter detection

Is reading mediated by soundrepresentations?

COUCH inhibits TOUCH while TRIBEmarginally primed BRIBE (Meyer et al. 1974)

M100 M170 M250 M350100-150ms 150-200ms 200-300ms 300-400msAveraged response to

visual words

Magnetoencephalographic (MEG)measures of visual word processing

Manipulating early and late(r)factors in letter processing

LP, Aug 03, Tateshina

M100 source (M100 source (““Type 1Type 1””))

More activity for noisy and long letter and symbol strings.More activity for noisy and long letter and symbol strings.

LP, Aug 03, Tateshina

Left hemisphere M170Left hemisphere M170

sourcesource

Activity delayed or decreased for less detectable Activity delayed or decreased for less detectable letterstringletterstringstimuli and in general stronger for letter strings than for symbolstimuli and in general stronger for letter strings than for symbolstringsstrings

LP, Aug 03, Tateshina

More activity for longer stimuli and noisy stimuli.More activity for longer stimuli and noisy stimuli.

Right hemisphere M170Right hemisphere M170

sourcesource

Left fusiform gyrus(The Visual Word Form Area, VWFA)

McCandliss, Cohen and Dehaene, The visual word form area: expertise for reading in the fusiform gyrus. Trends Cogn Sci. 2003Jul;7(7):293-299.

“Classic” view:

Activated by words and pseudowords to a greater degreethan other similar control stimuli.

Specific to the visual modality.

Insensitive to lexical factors (such as frequency).

Activated more by pseudowords than by consonantstrings.

Left fusiform gyrus(The Visual Word Form Area, VWFA)

Cohen, S. et al. The visual word form area: Spatial and temporal characterizationof an initial stage of reading in normal subjects and posterior split-brain patientsBrain 2000 123: 291-307.

Cohen, S. et al. The visual word form area: Spatial and temporal characterizationof an initial stage of reading in normal subjects and posterior split-brain patientsBrain 2000 123: 291-307.

Blurring the picture

A series of recent studies have shown that the leftfusiform gyrus shows activation in functionalimaging studies during a variety of lexical tasks,including naming, repetition, and Braille reading.

Price et al. (2003) and Price and Devlin (2003, 2004)

Blurring the picture

Hillis et al. (NeuroImage 24 (2005) 548–559)

Examined to what extent is the VWFA necessary,

sufficient, or specialized for processing of visualword forms by identifying deficits associated withacute damage or dysfunction of this region.

Activation of the left midfusiform gyrus in response to reading words and pseudowords is such a reliable finding infunctional imaging that this region has been called the visual word form are (VWFA). However, this label has recentlybeen challenged, because activation in VWFA is also observed in other lexical tasks. We evaluated whether VWFA isnecessary, sufficient, or specialized for reading by examining how frequently acute lesions in VWFA disrupt tasks thatrequire access to written word forms versus other lexical tasks. We administered lexical tasks with spoken and writteninput and output, and identified damage or dysfunction of VWFA and other regions of interest (ROI) on diffusion- and

perfusion-weighted imaging (DWI and PWI) in 80 patients within 24 h of onset of acute left ischemic stroke. Associationsbetween abnormalities in each region of interest and impairment on lexical tasks were evaluated with chi-squared tests.Damage or dysfunction of VWFA was not significantly associated with impairment ofwritten word comprehension or lexical decision, but was significantly associated with

impairment on all tasks requiring lexical output: oral reading and oral naming (visual ortactile input), and written naming. We account for these results and results from functional imaging by

proposing that the left midfusiform gyrus normally has two roles in reading: (1) computation of location- and modality-independent grapheme sequences from written word stimuli, and (2) a modality independent stage of lexical processingthat links modality-specific input and output representations. VWFA is not necessary for the former because the right

homologue of VWFA can immediately assumethis role.

Hillis et al. (NeuroImage 24 (2005) 548–559)

Blurring the picture

How are word recognition circuits organized in the left temporal lobe? We used functional magneticresonance imaging (fMRI) to dissect cortical word-processing circuits using three diagnostic criteria: thecapacity of an area (1) to respond to words in a single modality (visual or auditory) or in both modalities,(2) to modulate its response in a topdown manner as a function of the graphemic or phonemic emphasisof the task, and (3) to show repetition suppression in response to the conscious repetition of the target

word within the same sensory modality or across different modalities. The results clarify the organizationof visual and auditory word-processing streams. In particular, the visual word form area (VWFA) in

the left occipitotemporal sulcus appears strictly as a visual unimodal area. It is, however, borderedby a second lateral inferotemporal area which is multimodal [lateral inferotemporal multimodal

area (LIMA)]. Both areas might have been confounded in past work.

VWFA and case invariance

Fusiform face area

Right fusiform gyrus responds selectively to facesas opposed to other categories, such as hands,houses or animals (Kanwisher et al., 1997)

Does the FFA respond selectively to faces or toany category that humans have expertise on?

FFA and expertise

Would the FFAs of car and bird expertsrespond selectively to cars and birds?

Gauthier et al. (Nature Neuroscience, 2000): Yes! fMRI evidence that objects of visual expertise (cars

and birds) activate the right FFA more strongly thannon-expertise stimuli.

A correlation between the level of behavioralexpertise and the strength of fMRI signal to the

expertise stimuli in the right FFA in a locationmatching test.

FFA and expertise

But surely cars and birds have faces!

As we become experts with a category, perhapswe start treating the stimuli as having faces…?

FFA and expertise

But surely cars and birds have faces!

Xu 2005: Sideways cars also activate the FFA.

It has previously been reported (Gauthier et al., 2000, Nat. Neurosci., 3:191--197) in a functional magnetic resonance imaging (fMRI)study that objects of visual expertise (cars and birds) activate the right fusiform face area (FFA) more strongly than nonexpertise stimuli,and it was argued that the right FFA is involved in expertise specific rather than face specific visual processing. This expertise effect,however, may be due to experts taking advantage of the ‘faceness’ of the stimuli: birds have faces and three-quarter frontal views of carsresemble faces. This expertise effect may also be caused by a biased attentional modulation: with a blocked fMRI design, experts mayattend more to a block of expertise than a block of non-expertise stimuli. In this study, using both side-view car images that donot resemble faces and bird images in an eventrelated fMRI design that minimizes attentional modulation, anexpertise effect in the right FFA is observed in both car and bird experts (although a baseline bias makes the birdexpertise effect less reliable). These results are consistent with those of Gauthier et al., and suggest the involvement of the right FFA inprocessing non-face expertise visual stimuli.

FFA and expertise

Greebles

Gauthier et al. (1999):After extensivetraining with‘greebles’ observersshowed a higherfMRI response inboth FFAs topassively viewed‘greebles’ thannovices.

FFA and expertise

Is greeble processing like face processing?

Gauthier et al. (Neuropsychologia, 2004):

If your face processing is intact, but the processing of othercategories (houses, cars) isn’t, how are you on Greebles?

CK: visual agnosia but intact face processing.

FFA and expertise

Is greeble processing like face processing?

CK performs worse than controls in object matching.

like controls in the face matching.

worse than controls in greeble matching.

But CK was not trained on Greebles! However, CK was both an airplane and toy soldier “buff” before his brain

injury, and in both instances he lost the ability to discriminate objectswithin these two categories (Moscovitch et al., 1997).

Faces vs. words in MEG

M100, M170 and the time course of face processing

Liu et al. (Liu et al. (NatureNeuroscienceNatureNeuroscience, 2002):, 2002):