Perceptual Strategy: a tale of
letters and shapes
Cees van Leeuwen
Laboratory for Perceptual Dynamics, KU Leuven
cees.vanleeuwen@ppw.kuleuven.be
In collaboration with
Thomas Lachmann
Kaiserslautern University of Technology
Overview
• Introduction: two ways in which knowledge
influences perception
• Reading deficits as a consequence of
learning the wrong strategy
• Differentiation in strategies between
nonletters and letters
• Conclusions
Two ways in which knowledge influences
perception
1. What we know influences what
we perceive
The figure is determined based on familiarity.
Peterson & Gibson (1993).
2. Knowledge influences how we
perceive
Perceiving items as shapes vs
perceiving items as letters
Habitual, as a result of learning to
read!
Are Letters Special?
They are perfectly natural!
If letters are normal, why do some children
have difficulty in learning to read and write?
Developmental
Dyslexia
Reading Errors
- Slowness of reading; problems in
understanding written materials
- Losing their Line
- Omissions, Repetitions, Substitution,
Insertions
- Distortions of Words, Parts of Words
- Reversal Errors: was ∞ saw b ∞ d
 ORTON (1925) Cardinal symptom
The Causes are unknown
After more than 100 years of experimental studies
------------------------------------------------------------------------------------------------------------Acoustic information processing
VERSUS
phonological deficit
versus
versus
Visual information processing
orthographical deficit
But perhaps it is both, or a more general deficit.
Thomas Lachmann’s Functional Coordination
Deficit model
Not a deficit of
automatization, but
automatization of the
wrong strategy
Our participants
57 third/fourth graders
School psychologists‘ diagnosis in Grade 2
Own diagnosis prior to experiment: Discrepancy Definition
(2 SD Reading time SLRT vs. Raven)
The Cardinal Symptom
b vs. d vs. p vs. q
Problem with visuospatial processing of
symbols?
Mental Rotation with Letters
Mental Rotation
mirrored
P
r
e
s
s
Cooper & Shepard (1973)
Rusiak, Lachmann, Jaskowski, van Leeuwen (Perception, 2007)
N = 16 Dyslexics
N = 12 Controls
R, F, G, e, k (0-180° in 45°)
“normal” oder “mirror images”?
Mental Rotation with Letters
1300
RT (ms)
1100
900
700
Dyslexics
Controls
500
0
45
90
Angle of Rotation
-Typical Mental Rotation Effect
-Group effect (> 100 ms)
-No Interaction (no visuospatial processing deficit)
135
180
The Cardinal Symptom
b vs. d vs. p vs. q
If the problem is not with visuospatial
processing, perhaps it has something
to do with the structure of the
configuration
SYMMETRY
Symmetry
• Makes your world simpler
• Simple patterns have few
alternatives
Rotation and Reflection
Symmetry Groups
Equivalence Sets (ES)
Equivalence Sets Size (ESS)
Garner Patterns
Task
• Serial
presentation of
pairs of stimuli
ISI = 500 ms
• Same or
different
• Irrespective of
pattern
orientation
General preference for Symmetry
Detailed model predictions possible from Degree of
Pattern Symmetry (ESS) and Degree of “Sameness”
(IM, CM, or NM)
Lachmann & van Leeuwen (2004) Scientific Psychology Series
Model Fit
Lachmann & van Leeuwen, 2005, Quarterly Journal of Experimental Psychology
Letters vs Shapes
Normals vs Dyslexics
Lachmann & van Leeuwen, 2007, Developm. Neuropsychology
Results
1100
1100
1000
1000
900
900
800
800
700
700
symmetric
600
asymmetric
Letters
Patterns
Normal reading children
No effects on error rate
RT (ms)
RT (ms)
Material**; Symmetry**; Group*; Material x Symmetry x Group **
symmetric
600
asymmetric
Letters
Patterns
Dyslexics
No effects on error rate
Model fit*
1200
1100
1000
900
800
Dyslexics
RT (ms)
700
Normal
Readers
600
600
700
800
Predicted RT (ms)
900
1000
1100
*Note on Model fit
• Model fit was based on different assumptions for
Normals and Dyslexics
• Degree of symmetry for patterns was counted for both
Normals and Dyslexics
• Degree of symmetry for letters was counted for
Dyslexics but ignored for Normals
• Dyslexics are faster because they give equal importance
to Symmetry in Letters and Shapes
------------
Dyslexics:
• Outperform normal readers on this task
• The task involves letters
• Why don’t dyslexics read better than
normals?
Symmetry?
• Symmetry helps in perceiving shapes, but
hinders in perceiving letters
 letter symmetry may be
suppressed actively
• Strategy, based on reading practice
• When learning to read is difficult  anomalous
strategies
Configurations
Configurations
( (
((
()
Emergent Properties
(J.R. Pomerantz)
Configurations
Difficulty of recognizing the letter “E” when embedded in a Good
figure
Push the button on the
Right
GREEN
RED

Some Congruence Effects
Letters vs Shapes
Letters
versus
Shapes
Congruent
versus
Incongruent
Binary Classification
480
475
470
465
460
Congruent
Incongruent
455
450
445
440
435
Letters
Shapes
Van Leeuwen & Lachmann, Perception & Psychophysics, 2004
Binary Classification
490
480
470
460
Congruent
Incongruent
450
440
430
420
410
Letters
Rotated Letters Pseudo-Letters
Van Leeuwen & Lachmann, Perception & Psychophysics, 2004
Binary Classification
• Rotated letters Pseudo-letters, and Geometrical
Shapes show Congruence Effects.
• Letters show Negative Congruence Effects.
• Is the effect related to the response alternatives?
Contrasting
Response Categories
Similarity
Press Left Button: C or Circle or L or Rectangle
Press Right Button: H or Square or A or Triangle
No Similarity
Press Left Button: C or Square or L or Triangle
Press Right Button: H or Circle or A or Rectangle
Contrasting
Response Categories
600
495
490
500
485
400
480
Congruent
Incongruent
300
200
Congruent
Incongruent
475
470
465
100
460
0
455
Letters
Similarity
Shapes
Letters
Shapes
No Similarity
Binary Classification
In normal adult readers:
Dissociation in Early Visual Integration
Processes of Letters and Shapes
• What about less experienced readers?
• What about developmental dyslexics?
Dyslexic
Children
600
RT (ms)
590
Normal Reading
Children
580
570
CONINCON
560
560
RT (ms)
550
95% CI RT
540
520
CONINCON
iso
540
con
530
incon
520
N=
638
620
letter
500
95% CI RT
iso
480
con
incon
460
N=
547
531
letter
MATERIAL
541
546
553
shape
642
669
651
648
shape
MATERIAL
•Weaker dissociation in normal children
than in adults
537
•Dyslexics have increased response
times and variance AND an adult
dissociation pattern
 PUZZLE
Puzzle
Normal reading children have a weaker
dissociation than adults  strategy
differentiation not yet well established?
Dyslexics probably do not have more reading
experience  dissociation should be same or
even weaker
Quod Non!
Puzzle
Our Dyslexics sample has:
-slow response rates
-strong dissociation
Does this mean that all individuals in the sample
have both these characteristics?
Puzzle
Perhaps:
-slow response rates  Subpopulation I
-strong dissociation  Subpopulation II
Subtypes of Dyslexia?
Analogy with Lachmann (2003, 2005)
Puzzle
Diagnostic subgroups
Reading test: SLRT (Landerl, Wimmer, & Moser, 1997)
word and non-word reading subtests
Non-Word Reading Impaired (NWRI):
at least reading time in non-word reading > 2 SD
Frequent Word Reading Impaired (FWRI):
reading time in frequent word reading > 2 SD, but normal
non-word reading time (within 1 SD)
Puzzle
FWRI
NWRI
Fuchs &
Lachmann (2003)
Delayed auditory/visual
syllable discrimination
Pronounced fast-same
effect in visual conditions
Lachmann (2007)
Delayed letter
identification
Large modality effects
Lachmann et al.
(2005)
Attenuated mismatch
negativity syllables
Normal mismatch negativity
increased response times
but normal between
conditions effects
specific effects enhanced
mostly involving
visuo-auditory coordination
Same-Different Task
• Sequential presentation of
two items
• First always isolated,
second isolated or in
congruent or incongruent
surroundings
• Letters, Pseudo-letters,
Shapes; No mixed-category
pairs
• Adults, normal reading
children, FWRI vs NWRI
dyslexics
.
Material x congruence x group
Group
Normal reading
adults
Normal reading
Children
FWRI-dyslexics
NWRI-dyslexics
Material
Congruence
Isolated
Congruent
Incongruent
Letters
478
483
483
Pseudo-letters
501
498
515
Shapes
459
482
519
Letters
690
673
722
Pseudo-letters
698
737
771
Shapes
694
724
746
Letters
1006
965
1059
Pseudo-letters
990
1015
1085
Shapes
1016
1035
1122
Letters
745
836
755
Pseudo-letters
792
797
774
Shapes
712
784
842
Summary
• No differences in visuospatial manipulation
• Dyslexics sometimes even better than Normals
• Letter/Non-letter Dissociation
• Anomalous in Dyslexics
• Subgroups can be identified:
-- “General Slowing down” in FWRI
-- Enhanced Dissociation in NWRI
Hot from the Press
Fernandes, T., Vale, A.P., Martins, B., Morais, J., & Kolinsky, R. (2014) Processing in
Developmental Dyslexia: Combining evidence from dyslexics, typical readers and
illiterate adults. Developmental Science.
To clarify the link between anomalous letter processing and developmental
dyslexia, we examined the impact of surrounding contours on letter vs. pseudoletter processing by three groups of children – phonological dyslexics and two
controls, one matched for chronological age, the other for reading level – and
three groups of adults differing by schooling and literacy – unschooled illiterates
and ex-illiterates, and schooled literates. For pseudo-letters, all groups showed
congruence effects (CE: better performance for targets surrounded by a
congruent than by an incongruent shape). In contrast, for letters, only dyslexics
exhibited a CE, strongly related to their phonological recoding abilities even after
partialling out working memory, whereas the reverse held true for the pseudoletter CE. In illiterate adults, the higher letter knowledge, the smaller their letter
CE; their letter processing was immune (to some extent) to inference from
surrounding information. The absence of a letter CE in illiterates and the positive
CE in dyslexics have their origin in different aspects of the same ability, i.e.
phonological recoding.
A straightforward replication but with more straightforward results
Conclusion
Possible
mechanisms:
•Letter treated same
as non-letter shapes?
•Problems with
surrounding noise
suppression?
Thanks to:
• Prof. Thomas Lachmann, TU Kaiserslautern
and his students: Jessika Wüst, Katrin Berg, Sabine Jenke, Sandra
Schlademann, Patricia Rusiak, Dave Barton e.a.
• Third Primary School Leipzig
…and to you for your patience!