HOWARD ET AL (1992)
“The cortical localization of the lexicons: PET evidence.”
The results are consistent with the localization of a lexicon for spoken word recognition
in Wernicke’s area and a lexicon for written word recognition further back in the
temporal lobe. [very close the the angular gyrus, the classical localization of visual word
forms: Dejerine, 1891]
The proposal for the location of a visual word-form system differs from that by Petersen
et al (1990), who identified this in left medial extrastriate cortex. There was
however a weak trend implicating this location in the present study, some apparent
involvement of the left temporal region in Petersen et al’s (1990) data.
Subjects were 12 normal r-handed adults. Each S had six scans in a
session of 90 mins., one each control task, and two scans for each experimental task.
- Word reading (visual presentation +speaking)
- Word repetition (auditory presentation + speaking)
- “see and say”: a series of “False-font” stimuli: Ss required to say the
word “crime” after each control non-word, non-letter visual stimulus.
- “hear and say”: auditory presentation of words re-recorded backwards, and
Ss required to say “crime” after hearing each non-word auditory stimulus.
Sensory Processing. Comparing the activation patterns for same verbal response
given to false-font visual stimulation and words recorded backwards suggests that the
letter-like strings evoke bilateral activation in primary and secondary visual cortex
(striate and extrastriate areas) whereas the arbitrary auditory stimulation activate primary
and secondary auditory cortex.
Visual word processing. When word reading is compared with “see and say”
(false-fonts, š say “crime”) the significant difference in activation is in the
left temporal lobe (posterior middle temporal gyrus)
Auditory word processing When word repetition is compared with “hear and
say” (words backwards š say “crime”) the significant difference in activation is again in
the left temporal lobe: close to be slightly in front of the classical location of Wernicke’s
- The findings argue against the hypothesis that the processing of written words activates
representations in the auditory word-form system.
- The data lead to the hypothesis that “access to the lexicon for spoken words is a function
of Wernicke’s area” (the middle part of the left superior and middle temporal gyri)
- And also that “access to the lexicon for written words depends on an area about 16mm
away in left posterior middle temporal gyrus.” — on margin of the angular gyrus.
- The results correspond reasonably well with classical neuropsychology: lesion data from
patients with disorders of spoken and written word recognition.