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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5253_Библиотеки_им_академика_М_И_Перельмана.pdf
proceeds to V4 and further on to the inferior temporal cortex (ITC).
Reproduced from Archer, et al. (2020)6 under Creative Commons License.
Table 5.1. Comparison of magnocellular (dorsal) and parvocellular
(ventral) pathways and subsystems.*
Characteristic
Magnocellular-dorsal
(M-D, transient)
pathway
Parvocellular-ventral
(P-V, sustained)
pathway
Type of cell in the
optic nerve
Magno (M-cells)
Parvo (P-cells)
Pathway and
ultimate
destination in the
brain
Dorsal pathway to
parietal lobe (this part of
the brain covers about
the same area as a
cardinal’s skullcap)
Ventral pathway to
temporal lobe (the
part of the brain
adjacent to the temple
and ear)
Sensitivity to
movement and
flicker
Very sensitive
Insensitive
Ability to resolve
detail
Good at resolving coarse
detail
Good at resolving fine
detail
Ability to detect
contrasts
Sensitive to low contrast
images
Sensitive to high
contrast images
Effect of blur
Relatively insensitive to
blur
Greatly affected by
blur
Area of visual field
where most
sensitive
Peripheral vision
Central vision
Persistence of
response to a
stimulus
Nerve cells respond
briefly at the onset and
offset of a stimulus
(transient)
The response of the
nerve cells persists
throughout the
stimulus (sustained)
Ability to
discriminate
colours
Unable to discriminate
colours
Good at discriminating
colours
Chapter 5 The magnocellular-dorsal (M-D) deficit and associated theories
109
In recent years, a great deal has been written about the ‘M-D deficit
Vision, Reading Difficulties and Visual Stress
110
associated with reading difficulty’ and sometimes it seems to be
assumed that the ‘M-D system’ is a discrete entity which is invariably
associated with reading difficulty. An early, but authoritative, review by
Merigan and Maunsell highlights several of the misconceptions that
seem to have grown more recently around the concept of parallel
visual pathways.7 For example, the review highlights considerable
overlap in the functions of these two pathways, and many
interconnections between them. The M-D deficit hypothesis is
undoubtedly an oversimplification.8 A large number of psychophysical
tasks have been used in research studies to measure M-D function:
1. Contrast sensitivity function (CSF): the ability to perceive faint
(low contrast) objects (typically gratings) of different sizes (width
of gratings, measured in cycles per degree).
2. Temporal contrast sensitivity function (temporal CSF): a
measurement of the sensitivity to contrast (i.e., modulation
depth) as a function of time. This can be achieved by presenting
stimuli that vary sinusoidally over time (flicker).
3. Counterphase flicker: a grating flickers so that the light and dark
areas reverse contrast.
4. Temporal integration: an assessment of the ability to combine
information over time to improve detection or discrimination.
5. Critical flicker fusion frequency: the frequency at which a
flickering light is perceived as continuous.
6. Frequency doubling technique: a method of testing the visual
field in which a low spatial frequency (coarse, 0.25 cycles per
degree) sinusoidal grating flickers in a counterphase fashion at
a high temporal frequency, causing the illusion that the spatial
frequency of the grating has doubled.
7. Visible persistence: tests that measure the extent to which the
visual perception of a stimulus continues after termination of
the stimulus.
8. Visual backward masking: a method that presents one visual
stimulus (a "mask" or "masking stimulus") immediately after a
brief (typically 30 milliseconds) "target" visual stimulus resulting
in a failure to consciously perceive the first stimulus.
9. Uniform field flicker masking: a measurement of the contrast
required to detect a grating on a field of temporally modulated
(flickering) light.
10. Metacontrast masking: this is a specific type of masking in which
the target and mask have no overlapping contours (the mask is
spatially adjacent), and the mask is presented after the target.
11. Lateral masking: the extent to which the peripheral perception
of a visual stimulus (target) is impaired when other stimuli
(distractors) are present in its adjacent surroundings.
12. Line-spread function: the threshold for the detection of a
central line is determined as a function of the distance between
this central line and two lower contrast flanking lines.
13. Coherent dot motion: this uses a random array of moving dots,
most of which move randomly, but a given proportion of which
move coherently in one direction. The detection of the coherent
motion depends upon this proportion.
14. Coherent form motion: this task is somewhat similar to
coherent dot motion (described above), but instead of dots
there is an array of lines, most of which are orientated randomly
but a proportion of which are orientated coherently. The
detection of coherent form depends on this proportion.
Chapter 5 The magnocellular-dorsal (M-D) deficit and associated theories
111
In a few studies some of the stimuli detailed above have been used
with physiological measures including visual evoked potentials (VEP)
and functional magnetic resonance imaging (fMRI).
There are 14 tasks listed above that -called
M-D function and many do not correlate highly with one another,
9-11
same neural substrate.
have been used to measure so
raising doubts as to whether the tasks probe the
.2Table 5 summarises research on this subject, which is described in
more detail below.
Vision, Reading Difficulties and Visual Stress
112
Table 5.2. Summary of research on the M-D deficit in dyslexia*
Study
Sample
Confounders
controlled for
Test of M-D function
(see above table for
explanation)
Supports
M-D deficit
in RD?
Supports causal
role in RD (if
addressed)?
Lovegrove et al.
(1980)
12
10 dyslexic & 10 control boys
Age, sex, IQ,
socioeconomic
status
CSF (0.15 to 1.0 sec
exposure)
Yes
Lovegrove et al.
(1980)
13
15 dyslexic & 15 control
children
Age, IQ,
socioeconomic
status
Visible persistence
(initially called duration of
visual information store)
13
14
Yes
Badcock et al.
(1981)
14
12 dyslexic & 12 control boys
9 dyslexic & 9 control boys
Age, sex, IQ
Visible persistence
Yes
Lovegrove et al.
(1982)
15
5 dyslexic & 5 control boys
14 dyslexic & 14 control boys
Age, sex, IQ
CSF
Yes
Hoien (1982)
16
58 dyslexic & 54 control
children
Age, IQ,
educational
environment
Visible persistence
Yes
Di Lollo et al.
(1983)
17
10 dyslexic & 10 control boys
Age, sex, IQ
Visual backward masking
Yes
Martin et al.
(1984)
18
14 dyslexic & 14 control boys
Age, sex, IQ
CSF
Yes
Slaghuis et al.
(1984)
19
12 dyslexic & 12 control boys
Age, sex
Visible persistence
Yes
Chapter 5 The magnocellular-dorsal (M-D) deficit and associated theories
113
Lovegrove et al.
(1986)
20
123 pre-readers (cross-
sectional)
Cross-sectional
CSF
Yes
Yes
Martin &
Lovegrove
(1987)
21
15 dyslexic & 15 control boys
14 dyslexic & 14 control boys
Age, sex, IQ
Temporal CSF
(counterphase flicker)
Yes
Martin &
Lovegrove
(1988)
22
14 dyslexic & 14 control boys
14 reading-matched controls
Age, sex, IQ
Uniform field flicker
masking
Yes
May et al.
(1991)
23
May et al.
(1992)
24
10 dyslexic & 10 control boys
Age, sex, IQ
VEPs to gratings
Yes
Slaghuis et al.
(1992)
25
15 dyslexic & 15 control
children
Age, sex, IQ
Metacontrast masking
Yes
Slaghuis et al.
(1993)
26
35 dyslexic & 35 normal boys
Age, sex
Visible persistence
Yes
Casco (1993)
27
29 disabled readers & 29
controls
Age, sex, IQ,
socio-economic
status
CDM
Yes
Evans et al.
(1994)
9
39 dyslexic & 43 control
children
Age, sex, IQ,
educational
opportunity
CSF, flicker detection
Yes
No
Walther-Muller
(1995)
28
17 dyslexic & 17 control
children
Age, sex, IQ
Temporal CSF, line spread
function, visible
persistence, short-range
motion
No, except
in small sub-
group
Vision, Reading Difficulties and Visual Stress
114
Felmingham &
Jakobson
(1995)
29
9 dyslexic & 9 control boys
Age, sex, IQ
Flicker detection (2 cpd
counterphase flicker),
CDM (letter)
Yes
Cornelissen et
al. (1995)
30
29 RD & 29 control children
Age, IQ
CDM
Equivocal
Hogben et al.
(1995)
31
12 specific reading disability
& 12 control children
Age, IQ
Temporal integration
No
Eden et al.
(1996)
32
6 dyslexic & 8 control adults
Age, IQ, & other
behavioural
measures
CDM & fMRI
Yes
deficit
subtle
Deficit too subtle
to be causal
Johannes et al.
(1996)
33
6 dyslexic & 6 control adults
Age, sex, IQ
VEPs to transient &
steady-state
checkerboard reversals
No
Barnard et al.
(1998)
34
206 children, cross-sectional
Age
Flicker contrast sensitivity
No
Talcott et al.
(1998)
35
18 dyslexic & 18 control
adults
Age, sex, IQ
CDM, critical flicker fusion
frequency
Yes
Cornelissen et
al. (1998)
36
58 unselected children,
cross-sectional
Age, IQ, reading
ability
CDM
Yes
Yes
Cornelissen et
al. (1998)
37
Adults, 24 good at CDM & 24
bad at CDM
Age, IQ, reading
ability
CDM
Yes
Witton et al.
(1998)
38
21 dyslexic & 23 control
adults
Age, IQ
CDM
Yes
Slaghuis & Ryan
(1999)
39
15 dyslexic & 15 control
children
Age, sex, IQ
CSF, CDM, visible
persistence
Yes, only in
dysphoneid
ectic
Chapter 5 The magnocellular-dorsal (M-D) deficit and associated theories
115
subgroup
Keen et al.
(2000)
40
18 dyslexic, 18 control, & 18
reading-age matched
controls
Age, sex, IQ
Temporal processing of
visual information
Yes
Talcott et al.
(2000)
41
32 unselected children
(cross-sectional)
Age, IQ
CDM
Yes
Kiely et al.
(2001)
42
49 dyslexic, 40 low IQ, 149
controls
Age
CDM
No, low IQ
group worse
than
dyslexics
Heim et al.
(2001)
43
22 dyslexic & 11 control
children
Age & IQ
Visual temporal order
No
Ridder et al.
(2001)
44
21 dyslexic & 19 control
adults
Age & sex
CDM
Yes (in all
sub-types)
Pammer &
Wheatley
(2001)
11
21 dyslexic & 19 control
children
Age (IQ in
normal range)
FDT
Yes
Ben-Yehudah
et al. (2001)
45
38 dyslexic & 42 control
adults (subset in 2
nd
experiment)
Age & IQ (by
some
measures)
CSF (drifting gratings &
flickering gratings)
Yes
Hansen et al.
(2001)
46
15 dyslexic & 34 control
adults
Age & IQ
CDM & CFM
Yes; only
with CDM,
not CFM.
Amitay et al.
(2002)
47
30 RD & 30 control adults
Age
Drifting gratings, flicker
detection, speed
discrimination, CDM
No
Vision, Reading Difficulties and Visual Stress
116
Laasonen et al.
(2002)
48
16 dyslexic & 16 control
adults
Age & IQ
Temporal processing
acuity
Yes
No
Bednarek &
Grabowska
(2002)
49
21 dyslexic & 28 control
children
Age & IQ
CSF – static & dynamic
Yes
Williams et al.
(2003)
50
20 dyslexic & 23 control
children
Age & IQ
Flicker detection
No
Solan et al.
(2003)
51
27 RD & 23 control children
Age
CDM
Yes
Edwards et al.
(2003)
52
Cross-sectional, adults, 24 RD
& 22 controls
Age, IQ, VA
FDT
No
Sperling et al.
(2003)
53
19 dyslexic & 19 control
children
Age & IQ
Flicker rate for shape
identification
Yes
Yes (M-D function
correlated with
orthographic skill)
Buchholz &
McKone
(2004)
54
10 dyslexic & 10 control
adults
Age & IQ
FDT
Yes (normal
on acuity
task)
Wilmer et al.
(2004)
55
19 dyslexic & 17 control
adults
Age
CDM, CFM, velocity
discrimination
Yes, but two
types of
motion
processing
deficit
Sperling et al.
(2005)
56
28 dyslexic & 27 control
children
Not matched in
age or IQ
CSF (static & phase
reversal flicker)
No
Sperling et al.
(2006)
57
27 dyslexic & 28 control
adults
Age, not IQ
CDM (with and without
noise)
No (deficit
only when
Chapter 5 The magnocellular-dorsal (M-D) deficit and associated theories
117
32 dyslexic & 27 control
children
Not age or IQ
noise
present)
Hutzler et al.
(2006)
58
13 dyslexic & 13 control boys
Sex
CDM
No
Pernet et al.
(2006)
59
12 dyslexic & 12 control
adults
Age, sex (IQ in
normal range)
Lateral masking
Yes
White et al.
(2006)
60
23 dyslexic & 22 control
children
Age & IQ
CDM, CFM
No
Solan et al.
(2007)
61
23 RD & 19 control children
Age
CDM
Yes
No
Kevan &
Pammer
(2008)
62
24 dyslexic & 48 control
children
Age
FDT
Yes
Kevan &
Pammer
(2008)
63
Pre-reading children: 20
family history dyslexia, 42
controls
Age (IQ in
normal range)
CDM, CFM, FDT
Yes
Meng et al.
(2011)
64
27 dyslexic & 27 control
children
Age & IQ (also
cross-sectional
study 100
children)
CDM
Yes
Partial: CDM
accounts for 11%
of variance in
orthographic
judgement
Olulade et al.
(2013)
65
14 dyslexic & 14 control
children & 12 dyslexic RA-
matched controls
Age (or RA),
age-matched
groups were
not matched
for IQ
CDM & simultaneous
fMRI
Yes
No
Vision, Reading Difficulties and Visual Stress
118