Form- and Meaning-based Priming Effects in fMRI
§
Gonnerman ,
H. Jamison*, L.
P. Matthews* & J. Devlin*
Skilled reading is a complex cognitive task, which
engages a spatially distributed network of regions.
Attempts to relate individual anatomical regions with
particular types of processing typically rely on setting
explicit judgement tasks, such as classifying a word
based on form (orthography) or meaning (semantics).
However, the results may be contaminated by strategic
processing.
Priming paradigms offer an alternative approach. They
allow the relationship between words to be varied
without the awareness of subjects, in order that strategic
processing effects are avoided.
Priming occurs when one word alters our reaction to
another. If prime and target are related, this often leads
to a response time advantage.
Prime and target pairs may be related in:
(B0=3T, TR=3s, TE=30ms, 4x4x5mm). Images realigned
and registered to MNI152 template, smoothed with 5mm
FWHM Gaussian filter. FSL software* used to compute
random effects model.
Activations identified at Z>3.09, limited to areas engaged
by word reading (i.e. those inclusively masked with a
[unrelated words – non-words] contrast).
Subjects responded significantly faster to both
orthographically and morphologically related word pairs,
than to those which were unrelated (see Figure 2).
A trend towards a priming effect occurred for
semantically related word pairs.
Change in RT (ms)
meaning  semantics
form + meaning  morphology.
2. Current Study – Aims
In this study we employed a visual masked priming
paradigm to investigate automatic facilitation due to
shared form and/or meaning, in a 2x2 factorial design,
using event-related fMRI.
-0.2
-0.4
L. MTG
Orth
Morph
Sem
Priming Condition
b
0.0
-0.2
-0.4
Orth
Morph
Sem
*
0
Figure 4 – Neural Effects of Priming (a) There was a
reliable priming effect in the left middle temporal gyrus
(L. MTG) when words were semantically related and a
trend for morphological pairs. (b) Both orthographic
and semantic priming affected left inferior temporal
gyrus (L. ITG).
5. Summary
*
Response time is reduced significantly in
-10
Related in form
Related in meaning
-20
orthographic and morphological conditions.
Activation is reduced in several areas, for priming
-30
Orth
Morph
Sem
Priming Condition
Figure 2 – Behavioural Effects of Priming Mean
change in response time (RT) in each priming condition,
compared with unrelated word condition (given as 0ms
for comparison). * indicates p<.05.
(ii) Priming causes reductions in activation
relative to the unrelated condition. Orthography and
semantics affect left temporal regions - potential areas
for processing meaning. Orthography also affects extrastriate regions implicated in form processing.
Morphological priming effects were found in the
bilateral angular gyrus. At a lower statistical threshold,
morphology also reduced activation in posterior visual
form areas and anterior temporal regions.
Several neural regions showed a decrease in activation
under priming conditions, when compared with the
unrelated word condition (see Table 2).
3. Paradigm
6. Conclusions
12 Subjects – healthy, right-handed, native British
speakers. Aged 18-25 years [21±2], 7M/5F.
Peak Z in each Condition
Region Affected by Priming
Orth
Lexical Decision Task – had to decide whether target
was word or non-word, and respond by button press.
Rapid presentation and forward masking ensured
subjects were unaware of primes. Stimuli presented as
follows (Figure 1):
Common to all priming:
L angular gyrus
R angular gyrus
Form-based effects:
L posterior fusiform
L ventral pre-motor
Meaning-based effects:
L middle temporal gyrus
Morph
Sem
Priming Paradigms are useful in defining implicit
4.12
3.37
language processing regions. They demonstrate the
partially separable effects of orthography and
semantics, uncontaminated by strategic processing.
4.13
3.14
3.13
3.21
3.78
3.16
??
Morphology does not affect any regions other than
??
those affected by orthography and semantics. This is
consistent with the claim that morphology is processed
by the convergence of form and meaning.
3.28
Form * meaning interaction:
*
1000ms
0.0
Priming Condition
(i) Priming causes reductions in response time
form  orthography
a
L. ITG
4. Results
relative to unrelated word pairs
1. Background
% BOLD signal
change relative to
unrelated word pairs
Image Acquisition – Gradient-echo EPI sequence
% BOLD signal
change relative to
unrelated word pairs
*Centre for Functional Magnetic Resonance Imaging of the Brain, University of Oxford, Oxford, UK
§Department of Psychology, Lehigh University, Bethlehem, PA, USA
L inferior temporal cortex
3.10
3.31
$%##$%$
500ms
conceal
33ms
HIDE
Table 2 – Neural Correlates of Priming. Peak Z
values of those areas activated in the word reading
condition, which showed a reduction in activation in the
priming conditions. (L = left, R= right).
200ms
(iii) Effect Sizes
Trials began with a fixation point, followed by forward
mask, prime and finally target. Trials ended with lexical
decision and button press, with inter-stimulus intervals
being self-paced.
8. References
% BOLD signal
change relative to
unrelated word pairs
Figure 1 - Order of Stimulus Presentation
a
6 Conditions – from which prime-target stimulus pairs
were taken in pseudo-random order (Table 1).
Relationship
[-orth, -sem]
[+orth, -sem]
[+orth, +sem]
[-orth, +sem]
[-orth, -sem]
[-orth, -sem]
Example Pair
legible-CROWN
corner-CORN
boldly-BOLD
cheerful-HAPPY
banjo-HEEN
viper-NDMG
Table 1 – Experimental Conditions
0.0
-0.2
-0.4
Orth
Sem
0.0
-0.2
-
-0.4
Orth
L. posterior fusiform
Morph
Priming Condition
Bilateral angular gyri
b
Condition
1. Unrelated
2. Orthographically rel.
3. Morphologically rel.
4. Semantically related
5. Pseudowords
6. Non-words
This work was supported by funding from the
Wellcome Trust & the MRC. HJ would like to thank the
Wellcome Trust. We would also like to thank all
subjects for their participation in the project.
Figures 3 and 4 depict several of the regions affected by
priming, and reveal the size of the changes in activation
compared with the unrelated word pairs condition.
% BOLD signal
change relative to
unrelated word pairs
LEXICAL DECISION: BUTTON PRESS
7. Acknowledgements
Morph
Sem
Priming Condition
Figure 3 – Neural Effects of Priming (a) Bilateral
angular gyrus was affected by all three priming
conditions. (b) The left posterior fusiform revealed a
significant priming effect for orthographically related
words a smaller effect for morphological pairs.
* http://www.fmrib.ox.ac.uk/fsl
Gonnerman, L. M., Andersen, E. A., & Seidenberg, M. S. (submitted). Graded
semantic and phonological similarity effects in priming: Evidence for a
distributed connectionist approach to morphology.
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