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Articles in PresS. J Neurophysiol (February 12, 2014). doi:10.1152/jn.00709.2013
Saccadic adaptation shapes visual
space in macaques
Svenja Gremmler1,2, Annalisa Bosco3, Patrizia Fattori3, Markus Lappe1,2
1) Department of Psychology, University of Münster, 48149 Münster,
2) Otto Creutzfeld Center for Cognitive and Behavioral Neuroscience,
University of Münster, 48149 Münster, Germany
3) Department of Human and General Physiology, University of Bologna, 40126
Copyright 2014 by the American Physiological Society.
Saccadic eye movements are an integral part of many visually guided
behaviours. Recent research in humans has shown that processes which control
saccades are also involved in establishing perceptual space: A shift in object
localization during fixation occurred after saccade amplitudes had been shortened or
lengthened by saccadic adaptation. We tested whether similar effects can be
established in non-human primates. Two trained macaque monkeys localized briefly
presented stimuli on a touch screen by indicating the memorized target position with
the hand on the screen. The monkeys performed this localization task before and
after saccade amplitudes were modified through saccadic adaptation. During
localization trials they had to keep fixation. Successful saccadic adaptation led to a
concurrent shift of the touched position on the screen. This mislocalization occurred
both for adaptive shortening and lengthening of saccade amplitude. We conclude
that saccadic adaptation has the potential to influence localization performance in
monkeys, similar to the results found in humans.
Saccades are so brief that the visual information is not fully processed until the
movement has ended. To keep saccades accurate, their motor commands are
continuously adjusted. If a saccade consistently overshoots its target, the amplitude
is shortened and if the saccade undershoots its target, the amplitude is lengthened.
This saccadic adaptation is driven by the mismatch between the observed visual
input after the saccade and the expected visual input predicted when the saccade
was planned (Wong and Shelhamer (2011); Collins and Wallman (2012)). In the
laboratory, a post-saccadic error can be induced artificially by shifting the saccade
target during the eye movement (McLaughlin (1967)). Studies using this paradigm
showed that saccadic adaptation occurs in humans and in monkeys with different
time scales (Deubel (1987); Frens and Van Opstal (1994); Albano (1996); Straube
In humans, saccadic adaptation changes not only saccade amplitude, but can also
affect the perceived location of objects. Such mislocalization has been found in hand
pointing and in perceptual reports, depends on the type of saccade that is adapted
and the adaptation direction (Moidell and Bedell
Kowler 1999; Awater et al. 2005; Collins et al. 2007; Cotti et al. 2007; Bruno and
et al. 2010). These findings suggest that internal representation of the environment is
not exclusively constructed from the visual input collected on the retina but that
knowledge about the eye movement that is required to look at an object contributes
to its perceived position (Collins et al. (2007); Zimmermann and Lappe (2010)).
Saccadic adaptation causes a dissociation between the physical location of an object
on the retina and the end point of the saccade that targets that object. This
separation might either be due to a modified calculation of the saccadic motor
command or to adjustments of the target representation during saccadic adaptation.
In the later case, saccadic adaptation does not just change amplitudes of eye
movements but changes already the representation of the surrounding scene during
fixation. In Zimmermann and Lappe (2010) human subjects were first adapted by
shifting the saccade target during the saccade. When adaptation was established,
the subjects had to localize briefly presented peripheral targets, while they hold
fixation on a presented fixation spot during the whole trial. No saccade was executed
in the localization trials and hence no motor output was produced. The subjects
localized the targets by indicating the perceived position on the presentation display
with a mouse pointer. After adaptive saccade lengthening subjects reported the
objects more eccentric. After adaptive shortening the effects on the perceptual report
depended on the adaptation procedure. Subjects reported the perceived location less
eccentric when the adaptation procedure involved a strong and persistent post
saccadic error. Since amplitude shortening in humans is faster and more efficient
than lengthening, it reduces the post-saccadic errors quickly during the adaptation
process. Different time courses of saccadic shortening and lengthening are also seen
in monkeys (see Hopp and Fuchs (2004) and Pelisson et al. (2010) for review), but
since overall saccadic adaptation is slower in monkeys, the development of the post-
saccadic error likely differs between humans and monkeys. Therefore, we were
interested in testing potential effects of adaptation on localization in monkeys.
2 Materials and Methods
Experiments were performed in accordance with national laws on care and use of
laboratory animals and with the European Communities Council Directive of 24th
November 1986(86/609/EEC) and with the Directive of 22nd September 2010
(2010/63/EU) and were approved by the Bioethical Committee of the University of
The head-restraint system on the head of the trained Macaca fascicularis was
surgically implanted in asepsis and under general anesthesia (sodium thiopental, 8
mg/Kg/h, i.v.) following the procedures reported in Galletti et al. 1995. Adequate
measures were taken to minimize pain or discomfort. A full program of postoperative
analgesia (ketorolac tromethamine, 1 mg/Kg i.m. immediately after surgery, and 1.6
mg/Kg i.m. on the following days) and antibiotic care [Ritardomicina (benzatinic
benzylpenicillin plus dihydrostreptomycin plus streptomycin) 1-1.5 ml/10 kg every 5-6
2.1 Recording of eye movements and stimulus presentation
During the experimental sessions, signals from both eyes were recorded
simultaneously with an infrared oculometer (ISCAN, Inc) at a sampling rate of 100
Hz. The monkey sat in a primate chair with its head restrained and it faced a 19 ”
touchscreen monitor (ELO, IntelliTouch 1939L) with a visible display size of 37.5 x
30.0 cm and 15500 touchpoints/cm2. The viewing distance of 28 cm from the
animal’s eyes to the screen resulted in a visual field of 53.3 x 47.0 deg. The display
had a resolution of 1152 x 864 pixels and a frame rate of 60 Hz. For stimuli
presentation we used MATLAB with the psychtoolbox extension (Brainard 1997). The
stimuli were green and red dots with a radius of 0.2 deg and vertical arranged yellow
2.2 Behavioral task
The two monkeys were trained to make memory guided reaching movements to a
briefly presented target stimulus on a touch screen. During localization training
sessions, to be rewarded, the monkeys had to hold gaze fixation on a fixation spot
and, after a go signal, they had to indicate the position of a briefly presented
eccentric target stimulus on the touch screen with their right hand. The position of the
target stimulus varied between 5 deg and 25 deg to the right of the fixation spot. The
animal needed to touch the screen at the horizontal position of the target stimulus +/-
1.0 deg and hold the fixation on the fixation spot at the same time to receive the
reward. Both monkeys used all four fingers of the right hand to touch the screen. The
training ensured that they were able to indicate the flashed position with a precision
After training we measured touch locations before and after manipulation of saccadic
amplitude by adaptation. The measurements were completed in two conditions. In
the first condition the saccadic amplitude was shortened and in the second condition
the amplitude was lengthened. In the beginning of each session, the animal
performed 20 localization trials in which it had to touch the target location during
fixation. The setup of a localization trial is described in Figure 1: Pre-adaptation
phase. The monkey pressed a button in front of its chest to start the trial and a green
fixation spot appeared. After a randomized time between 1.0 s and 1.7 s, a yellow
bar was flashed for 50 ms 18 deg to the right of the fixation spot. The monkey was
trained to keep fixation on the green spot. If the monkey broke fixation when the bar
was presented, the trial was aborted and the monkey did not receive any reward.
After another randomized time between 1.0 s and 1.7 s the fixation spot changed
color to red. This was the signal for the monkey to touch the screen in the position
where it had seen the flashed bar before. The monkey used its hand to indicate the
position of the flashed bar on the screen, while still holding fixation on the red spot. In
training sessions, before the experiment started, the monkey had to touch the screen
in a small window of 1 deg x 1 deg around the horizontal position of the flashed bar
to receive the reward. During the experiment, in which we expected that the touch
location might vary because of the prior adaptation, the monkey was allowed to touch
the screen at any position to receive reward. In this way, we avoided to reinforce any
bias of touched position while the data was collected. Furthermore, in localization
trials the monkey did not execute any saccade but had to hold fixation.
Our experiment tested localization for a bar flashed at the saccade target location.
We chose this position because it is known that adaptation is a local phenomenon
that spreads only moderately to neighboring locations (Frens and Van Opstal (1997))
and that the same is true for the associated localization effects in humans (Collins
et al. (2007); Schnier et al. (2010)). To ensure that the monkeys remain to report the
perceived bar position accurately the animals performed in the weeks before the
measurements and also in between the measurements several training sessions with
hundreds of localization trials. In these training sessions, the bar appeared at many
different positions and to be rewarded the monkey had to localize the flashed position
within a margin of 1 deg. Therefore, the monkey was enforced to continue reporting
accurately the perceived bar position without any strategic offsets during the whole
After measuring the baseline localization performance of the monkey in the pre-
adaptation phase, we manipulated the saccadic amplitude in the adaptation phase.
This phase consisted of 400 adaptation trials. The setup of adaptation trials is
pictured in Figure 1: Adaptation phase. After the monkey had pressed the button to
start the trial, a green fixation spot appeared for a randomized time between 0.7 and
1.5 s. If the monkey’s gaze did not enter a 4 deg x 4 deg window around the fixation
spot in less than 300 ms after the appearance of the fixation spot, or if the monkeys
gaze left that window for longer than 150 ms after entering, the trial was aborted, the
screen became black and the monkey did not receive any reward in that trial.
Provided that the monkey’s gaze successfully entered the fixation window and that it
was detectable inside the window the last 300 ms, the fixation spot disappeared
again after a randomized time between 0.7 and 1.5 s and simultaneously a green
target spot was presented 18 deg to the right from the fixation spot. The monkey then
had to make a saccade to the target. Saccade onset was detected, when the gaze
movement exceeded a distance of 3 deg from the fixation spot. As soon as saccade
onset was detected, the target was shifted to a new position to induce a post-
saccadic error. The maximum elapsed time between saccade onset and target shift
thus was composed of the time the eyes need to travel the first 3 deg of the saccade,
the sample time of the oculometer and the frame duration of the screen. The eyes
typically exceeded a distance of 3 deg to the fixation spot in less than 30 ms after
saccade onset and sample time and frame duration add up to maximal 27 ms.
Hence, the target shift occurred about 57 ms after saccade onset and thus before the
The target reappeared either shifted to the right or to the left, depending on the
condition, which was tested in the session. In the first condition, the target was
shifted 4 deg leftwards towards the fixation point. In this way, the monkey overshot
the new target position and the amplitude became shorter during the adaptation
phase. In the second condition, the target jumped 4 deg further to the right so that
the saccadic amplitude increased during the adaptation phase. In each session only
one condition was tested, thus either the amplitude was shortened or it was
lengthened. The structure of these trials was the same as the structure of the training
trials that the monkey had made in order to learn the saccade task. The only
differences were the target intra-saccadic target jump to induce the adaptation, and
the reward contingencies. In training trials without the intra-saccadic target jump the
monkey’s gaze had to enter a 6 deg x 6 deg window around the target position in
less than 150 ms after saccade onset detection and stay in that window for 200 ms.
Otherwise the trial was aborted and the monkey did not receive any reward. In
adaptation trials, reward was not contingent on the monkeys final gaze position since
we expected gradual change of amplitude and thus saccadic end position due to
adaptation during the session. However, in training as well as in adaptation sessions
the target turned red after a randomized time between 600 ms and 1000 ms after it
had appeared or was shifted. The color change was the signal for the monkey to
release the button that he had to press since the start of the trial. If the monkey
released the button within a maximum time of 1000 ms, the trial was ended
successfully and a defined amount of water was given as reward.
After the amplitude was successfully altered in the 400 adaptation trials, we tested
again the monkey’s object localization in a post-adaptation phase. This phase was
built up identically to the pre-adaptation phase. In the end we compared the mean
touched position in the pre-adaptation phase before the saccadic amplitude was
modified with the mean touched position in the post-adaptation phase after the
saccadic amplitude had been adapted. We refer to the difference between the two
mean touched positions as the adaptation induced mislocalization. Two sessions
were separated by at least 48 h to extinguish the induced adaptation before the next
2.3 Data analysis
Saccade trajectories during the adaptation phase were used to calculate the
amplitude of each saccade by determining gaze position directly before the saccade
onset at the time when the target was presented and the saccade ending position
when the velocity of the saccade dropped under the threshold of one-tenth of the
maximal reached velocity in that saccade. For the offline data analysis we used
MATLAB. Changes of localization position and saccadic amplitude were tested for
significance employing two-tailed t-tests with independent and paired samples.
To determine the adaptation time constants during saccadic shortening and
lengthening, the time course of adaptation in every session was fit with an
exponential function (see Figure 2): A
) = A
0 + G
0 is the asymptotic amplitude the monkey is approaching, G is the difference
of the baseline amplitude and the asymptotic amplitude, and t is the rate constant of
decay and increment during saccade shortening and lengthening, respectively.
In the first 10 trials of the adaptation phase the target stayed in place and was not
shifted in any direction. These first 10 saccadic amplitudes were used to calculate the
mean pre-adaptation amplitude, i.e. the baseline amplitude. Likewise, the last 10
trials of this phase were used to calculate the mean post-adaptation amplitude. This
post-adaptation amplitude then was used to calculate the deviation of the amplitude
In every session we first measured a baseline mean touched position for the flashed
bar before we altered the saccadic amplitude via saccadic adaptation. Moreover,
before calculating the saccadic amplitudes in the 400 trials of the adaptation phase,
we checked that the start positions at the beginning of the adaptation phase and the
end of the adaptation phase did not differ to ensure that any amplitude change during
the adaptation phase can be ascribed to landing point modifications rather than a
shift of the monkey’s fixation position inside the tracker window in the direction of the
future position of the saccade target. There was no significant difference between the
mean fixation position in the first ten adaptation trials of each session and the last ten
trials in both monkeys. Monkey one showed an insignificant mean shift in fixation
position of -0.18 deg +/- 0.6 deg (two-tailed paired t-test, p = 0.74) and monkey two
showed an insignificant opposed shift of 0.16 deg +/- 0.5 deg (two-tailed paired t-test,
p = 0.43). In Figure 2 two adaptation curves with saccadic shortening (A) and
saccadic lengthening (B) are presented. The time course of adaptation was fit with an
exponential function, to determine the time constants of adaptive change of the
Saccadic shortening is usually much faster than saccadic lengthening (Hopp and
Fuchs (2004); Pelisson et al. (2010)) and this was also the case in our data. In Figure
2 the time constants that are given for the two presented example sessions show that
the monkey adapted faster in the saccadic shortening session. The mean rate
constant for all sessions of both monkeys was t = 72.7 +/- 58.2 saccades for
saccadic shortening whereas for saccadic lengthening it was t = 249.3 +/- 196.6
saccades. The higher rate constant for saccadic lengthening indicates that
lengthening adaptation might not be fully saturated after 400 trials. A higher number
of adaptation trials would thus lead to stronger amplitude modification in amplitude
lengthening but would have only little or no effect on the induced amount of
adaptation in amplitude shortening. After the saccadic amplitude had been modified,
we measured again the touched position on the screen in the localization trials. In
Figure 3 the positions that were touched by one monkey in the localization trials
before and after the saccadic adaptation phase are shown for two example sessions.
In the session displayed in Figure 3 A the saccadic amplitude was shortened and in
Figure 3 B the saccadic amplitude was lengthened. The 20 trials in the pre-
adaptation phase were used to calculate a mean pre-adaptation baseline position
and the 20 trials of the post-adaptation phase were used to calculate the mean
deviation in located position from the baseline.
The results from both monkeys are presented in Figure 4. The first animal completed
three sessions with amplitude shortening and four sessions with amplitude
lengthening. In the three sessions with saccadic shortening a significant mean
saccadic amplitude change of -2.9 +/- 0.7 deg (two-tailed t-test, p = 0.02) was
induced. The adaptation induced also a significant mislocalization compared to the
baseline localization of -1.4 +/- 0.5 deg (two-tailed t-test, p <
0.05). The amount of
induced mislocalization was significantly smaller than the saccadic amplitude change
In the four sessions with amplitude lengthening we found significant saccadic
amplitude change of 1.0 +/- 0.4 deg (two-tailed t-test, p = 0.01) and also an
adaptation induced mislocalization of 0.6 +/- 0.2 deg (two-tailed t-test, p = 0.01). In
contrast to amplitude shortening there was no significant difference between
saccadic amplitude change and mislocalization (two-tailed paired t-test, p = 0.15)
after amplitude lengthening. The total amount of mislocalization was 2.3 times higher
after amplitude shortening than after amplitude lengthening (two-tailed paired t-test, p
In the condition of adaptive amplitude shortening we found stronger adaptation than
in the condition of amplitude lengthening (two-tailed paired t-test, p = 0.01). The
amplitude change in the condition of amplitude shortening accounted for 70 % of the
4 deg target step while the amplitude change after amplitude lengthening accounted
only for 25 % of the 4 deg target step. Thus the saccades ended much closer to the
shifted target during amplitude shortening, inducing a smaller post-saccadic error
during the major part of the adaptation phase compared to amplitude lengthening.
The results from monkey two are presented in the right panel of Figure 4. This animal
completed four sessions with amplitude shortening and three sessions with amplitude
lengthening. Saccadic adaptation induced a significant mean saccadic amplitude
change of -2.7 +/- 0.6 deg (two-tailed t-test, p <
0.01) in the four sessions with
saccadic shortening. The adaptation also induced a significant mislocalization of -1.1
+/- 0.5 deg (two-tailed t-test, p = 0.03). Similarly to animal one, the amplitude change
and the mislocalization differed significantly (two-tailed paired t-test, p <
0.01) in the
In the three sessions of animal two with amplitude lengthening we found significant
saccadic amplitude change of 1.0 +/- 0.1 deg (two-tailed t-test, p <
0.01) and also an
adaptation induced mislocalization of 1.1 +/- 0.5 deg (two-tailed t-test, p <
in animal one there was no significant difference between saccadic amplitude change
and mislocalization (two-tailed paired t-test, p = 0.8) after amplitude lengthening. In
contrast to animal one animal two showed the same total amount of mislocalization
after amplitude shortening and lengthening (two-tailed paired t-test, p = 0.9).
Finally, in the condition of adaptive amplitude shortening we found again stronger
adaptation than in the condition of amplitude lengthening in this monkey (two-tailed
Two monkeys were trained to indicate the position of a briefly flashed stimulus with
their hand on a touch screen, while holding fixation on a presented fixation spot
during the whole trial. Both animals showed a significant offset in touched position
after their saccadic amplitudes had been altered, even though no saccade was
executed during these localization trials. We regard the positions at which the
monkey touched the screen as a measure of localization of the presented target, and
thus as an indicator of perceived position, similar to experiments in humans (Collins
et al. 2007; Zimmermann and Lappe 2009; 2010; Schnier et al. 2010). Alternatively,
one may consider the touch position as the end point of a reaching movement, i.e.
the result of another motor action. In this case, our findings demonstrate that
saccadic adaptation transfers to reaching movements, or that saccade and reaching
movements share a common representation of target location. However, in humans
effects of saccadic adaptation on perceived location have been shown with several
different methods (pointing (Cotti et al. 2007; Bruno and Morrone 2007; Hernandez
2008), verbal or perceptual report (Moidell and Bedell
et al. 2005), probe placement with a mouse pointer (Collins et al. 2007; Zimmermann
and Lappe 2009; Schnier et al. 2010)) suggesting that a common representation of
object location in all these cases is affected by saccadic adaptation.
The results of our study can be summarized in the following way. First, we found an
adaptation induced change in saccade amplitude in both conditions in both monkeys.
Second, mislocalization of the flashed stimulus occurred after adaptation in both
conditions in both monkeys. Third, this mislocalization was in all cases in the same
direction as the saccade amplitude change. Fourth, the saccadic amplitude change
was stronger after amplitude shortening than after amplitude lengthening in both
monkeys. Fifth, in one monkey the change of localization position was stronger after
amplitude shortening than after amplitude lengthening. This was not the case in the
other monkey. Finally, after amplitude shortening the change in localization position
was smaller than the change in saccade amplitude, whereas both changes were of
comparable magnitude after amplitude lengthening. This was true in both monkeys.
The differences in amplitude change between amplitude shortening adaptation and
amplitude lengthening adaptation provide further support for the view that saccadic
lengthening and shortening are based on partial different mechanisms within the
(1981); Semmlow et al. (1989); Straube and
Our findings on mislocalization show agreement with earlier results in human
subjects, but they show also some interesting differences. In the first experiment of
Zimmermann and Lappe (2010), which used the same adaptation paradigm as our
study, human subjects showed mislocalization only after lengthening adaptation but
not after shortening adaptation. Our findings in monkeys agree very well for saccadic
lengthening, but in contrast to humans, saccadic shortening also influenced
However, the second experiment of Zimmermann and Lappe (2010) showed that
mislocalization can also occur after shortening adaptation provided that a constant
error was applied throughout the adaptation trials. In this constant error adaptation,
the saccadic landing end point was calculated online while the saccade was
executed and the target was shifted to a position with a constant offset from the
Zimmermann and Lappe (2010) proposed that saccade adaptation for amplitude
shortening is so fast that the post-saccadic error is reduced too quickly to establish
effects on localization. Adaptive lengthening, which follows a slower time course in
et al. (2008a); Hernandez et al. (2008); Panouilleres et
(Straube et al. (1997); Cecala and Freedman (2009)), can lead to localization errors
through an adaptive change of saccade target representation that is slow and takes
effect only if a large post-saccadic error persists over a large number of trials. The
constant error paradigm established this situation also for saccade shortening in
humans, and hence leads to mislocalization also in this situation. This explanation
would be consistent with our result that normal saccadic shortening influences
localization in monkeys, since adaptation is generally slower in monkeys than in
et al. (1997); Watanabe et al. (2003)), leading to a longer persistent error during
saccade shortening adaptation in monkeys compared to humans.
It is well established that saccadic adaptation is not a singular mechanism but affects
multiple stages of the oculomotor transformation and that fast adaptive amplitude
shortening and comparatively slow adaptive lengthening must involve at least in part
different stages (see Hopp and Fuchs (2004) and Pelisson et al. (2010) for review).
Studies on adaptation time courses and dynamics suggested on the one hand a
forward model with adaptation via modifications of internal monitoring as a possible
adaptive mechanism and on the other hand direct modification of the saccade
steering motor command and thus of a target representation stage (Ethier
et al. (2008b); Chen-Harris et al. (2008); Xu-Wilson et al. (2009)). In the model of
Chen-Harris et al. (2008) a large post-saccadic error size, which occurs exceedingly
in slow adaptive lengthening, leads with increased probability to modifications of the
target representation stage. These modifications might moreover result in modified
target localization. Thus this size dependent error assignment could account for the
differences between adaptive shortening and lengthening and, furthermore, the
differences between fast adapting humans and slow adapting monkeys in adaptation
We conclude that saccadic adaptation affects localization in monkeys in a
comparable way as it affects localization in humans. Slower adaptation in monkeys
than in humans might lead to a stronger contribution of target representation stage
modifications to the adaptation process in monkeys that yields mislocalization after
both adaptive shortening and lengthening. Furthermore, the slower amplitude change
during amplitude lengthening than during shortening leads to longer remaining large
post-saccadic errors. These errors in turn may lead via error assignment to
modifications of the target representation stage and associated changes in
M.L. is supported by the German Science Foundation DFG LA-962/3, the German
Federal Ministry of Education and Research project Visuo-spatial Cognition and the
EC Project FP7-ICT-217077-EYESHOTS. P.F. is supported by the Fondazione del
Monte di Bologna e Ravenna and Ministero dell’Istruzione, dell’Universit_ e della
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Figure 1: One session consisted of three phases. In the pre-adaptation phase the
animals completed 20 localization trials. In the localization task the monkey had to
fixate on a green spot presented on the eye level of the monkey and 9 deg viewing
angle to the left. After a randomized time a yellow bar was flashed at 18 deg
eccentricity. After a following color change of the fixation spot the monkey indicated
the target position on the touchscreen while he maintained fixated. The following
adaptation phase consisted of 400 saccadic adaptation trials. In these trials the target
spot is shifted during the saccade and thus a mismatch between calculated post-
saccadic retinal target position and actual post-saccadic retinal target position is
induced . After the saccadic amplitude had been shortened or lengthened during the
adaptation phase the animal had to complete another 20 localization trials in the
post-adaptation phase to measure the deviation from the localization baseline
determined in the pre-adaptation phase. White circle: gaze position; dashed white
circle: previous gaze position; light/dark gray dot: fixation spot and saccade target
position; vertical bar: localization stimulus; hand shape: position of the correct
Figure 2: Examples of the adaptation phase: In one condition the animal’s
saccadic amplitude was shortened (A) and in the other condition the amplitude was
lengthened (B) via saccadic adaptation. The plots show the size of the saccadic
amplitude in every trial of one session (dots). The line represents a fit of the data with
the exponential function A
) = A
0 + G
. The rate constants of the adaptation
course in these two example sessions are t = 112.5 saccades for amplitude
shortening and t= 471.2 saccades for amplitude lengthening.
Figure 3: The positions of the flashed stimulus as indicated by one animal by
touching the screen in two example sessions. A) The indicated positions of a flashed
stimulus at 18 deg viewing angle before and after shortening of the saccadic
amplitude via saccadic adaptation. The pre-adaptation mean indicated position in this
session was 17.4 deg +/- 0.9 deg and the post-adaptation mean indicated position
was 15.6 deg +/- 2.0 deg. B) The indicated positions before and after lengthening of
the saccadic amplitude. The pre-adaptation mean indicated position was 17.1 deg +/-
1.2 deg and the post-adaptation mean indicated position was 18.0 deg +/- 1.3 deg.
Figure 4: The mean localization results from both animals. The dark gray bars
represent the mean adaptation level of each monkey in the inward adaptation
sessions in diagram A and the outward adaptation sessions in diagram B. The light
gray bars represent the mislocalization of the flashed stimulus in both adaptation
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