Double-Step Adaptation of Saccadic Eye Movements Is Influenced by Priming with Age Stereotypies

doi:10.4236/psych.2013.412147

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2013. Vol.4, No.12, 1014-1017

Published Online December 2013 in SciRes (http://www.scirp.org/journal/psych) http://dx.doi.org/10.4236/psych.2013.412147

Open Access

1014

Double-Step Adaptation of Saccadic Eye Movements Is

Influenced by Priming with Age Stereotypies

Otmar Bock1, Valentina Grigorova2, Milena Ilieva2

1Institute of Physiology and Anatomy, German Sport University, Köln, Germany

2Institute of Neurobiology, Bulgarian Academy of Sciences, Sofia, Bulgaria

Email: [email protected]

Received August 13th, 2013; revised September 16th, 2013; accepted October 12th, 2013

tribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the

original work is properly cited. In accordance of the Creative Commons Attribution License all Copyrights ©

are guarded by law and by SCIRP as a guardian.

Age related deficits of sensorimotor adaptation have been observed earlier with arm, but not with eye

movements. Here we evaluate whether deficits of eye adaptation may depend on the subjects’ believes

about their own sensorimotor abilities. To find out, elderly subjects were primed with positive or negative

age stereotypes using the scrambled-sentence task, and were then exposed to a double-step saccade adap-

tation task. The outcome was compared to data from an earlier study with unprimed elderly persons. We

found adaptation to be stronger after positive priming than after negative or no priming, with no differ-

ence between the latter two. Aftereffects of adaptation were not modified by priming. From this we con-

clude that positive primes enhanced workaround strategies, but not adaptive recalibration, while negative

primes failed completely, possibly because of a floor effect.

Keywords: Old Age; Plasticity; Strategies; Recalibration; Societal Stereotypies

Introduction

The human sensorimotor system adapts readily to a wide

range of distortions (Bock, 2013): when the visual or the force

environment is systematically altered, our behavior is initially

perturbed but gradually normalizes with extended practice. This

ability deteriorates in old age; however, it has been shown that

the speed and magnitude of adaptive change are reduced, while

aftereffects remain intact (Bock, 2005; Fernández-Ruiz, Hall,

Vergara, & Díaz, 2000; McNay & Willingham, 1998). Since

aftereffects are thought to reflect adaptive recalibration only,

unbiased by strategies (McNay & Willingham, 1998; Redding

& Wallace, 1996), the above work indicates that strategic con-

trol but not adaptive recalibration is degraded in old age. Accor-

dingly, age-related deficits of adaptive change were found to be

associated with cognitive decline (Bock & Girgenrath, 2006).

The above studies dealt with the effects of old age on the

adaptation of arm movements. We have recently expanded this

work to oculomotor saccades and found no age-related deficits

for saccadic adaptation under single-task conditions, nor under

dual-task conditions when the second task was spatially adja-

cent; an adaptation deficit only emerged when the second task

was located further away (Bock et al., under review). We at-

tributed that deficit to the well-known shrinkage of the attention

focus in old age (Ball & Owsley, 1993; Beurskens & Bock,

2012; Sekuler & Ball, 1986), and concluded that saccadic ad-

aptation per se is largely age-independent.

It seems surprising that saccadic adaptation should be im-

mune to age-related decay, while other characteristics of ocular

saccades deteriorate: their speed and accuracy decreases (Bono

et al., 1996; Paquette & Fung, 2011), and their path across a

visual scene becomes less efficient (Chapman & Hollands,

2006; Maltz & Shinar, 1999). In fact, elderly subjects in our

preceding study didn’t adapt as well as young ones (Bock et al.,

under review), only the deficit didn’t reach statistical signifi-

cance. With these arguments casting doubt on our earlier con-

clusion, we decided to scrutinize it with a fresh approach.

Following the arguments of others, we reasoned that sen-

sorimotor performance in old age is determined not only by

biological decay, but also by the actor’s confidence in her/his

own capacity. This has been shown by studies which manipu-

lated the self-confidence of seniors by priming them with so-

cietal preconceptions about the abilities of elderly persons:

positive age stereotypes (words such as “mature”) enhanced,

and negative ones (words such as “frail”) degraded seniors’

performance on tasks such as locomotion (Hausdorff, Levy, &

Wei, 1999), chair rising (Levy, 2000) and handwriting (Levy &

Leifheit-Limson, 2009). We hypothesized that saccadic adapta-

tion is affected by self-confidence as well, and therefore is im-

paired in elderly persons who assimilate negative societal

stereotypes towards old age, but not in those who assimilate

positive ones. This differential compliance with societal ste-

reotypes would increase intersubject variability, and thus might

have reduced the significance level for age differences in our

preceding adaptation study to below 0.05. To explore this view,

we now compare saccadic adaptation in elderly participants

primed with positive versus negative stereotypes of old age.

Methods

Sixteen healthy right-handed subjects participated. They

O. BOCK ET AL.

were 58.7 ± 4.4 year old, had normal or corrected- to- normal

vision, were native Bulgarian speakers with different education

levels, and were naïve to the purposes of the experiment. All

signed an informed consent to this study, which was pre-ap-

proved by the Ethics Committee of the Institute of Neurobiol-

ogy at the Bulgarian Academy of Sciences in Sofia.

Subjects were first primed with age stereotypes using an es-

tablished procedure, the scrambled sentence task (Bargh, Chen,

& Burrows, 1996). Each person was given 20 lists of five

words, and had to select four words from each list to formulate

a meaningful sentence; the fifth, non-fitting word had to be

crossed out. Unbeknown to the subjects, one of the four se-

lected words was either a positive or a negative age stereotype

(e.g., “wisdom” versus “decay”). Eight subjects received lists

with positive stereotypes, and the other eight with negative ones;

all were instructed to proceed at their own pace. The prime

words came from a pilot study in which eight persons, aged 50

to 65, rated a list of 15 experimenter-selected words on two

ten-point Likert scales, one scale for “maturity” and the other

for “frailty”. The 10 words with the highest “maturity” rating

(5.0 to 8.0) and the 10 with the highest “frailty” rating (6.3 to

8.3) were repeatedly used as primes for the main experiment.

The scrambled sentence task was followed by a saccade ad-

aptation task, using procedures established in our earlier work

(Bock, Schmitz, & Grigorova, 2008; Grigorova, Bock, & Bo-

risova, 2013). In single-step trials, a target of 7 mm diameter

was presented in the center of the screen for 750 - 1500 ms,

enclosed by a circle of 11 cm radius. The target then jumped

onto the circle in one of eight randomly selected directions (0,

45, 90, 315 deg, where 0 deg denotes rightwards, and 90 deg

upwards), and returned to the center 760 ms later. In dou-

ble-step trials, the target jumped onto the circle, shifted along

the circle by −15 deg (clockwise) after 200 ms , and returned to

the center 640 ms later. Twenty successive trials constituted an

episode, and were separated from the next episode by a short

rest break. The adaptation task consisted of a baseline phase

with two single-step episodes, followed by an adaptation phase

with 25 double-step episodes, and then by an aftereffect phase

with two single-step episodes.

The data of eight subjects from another study (Bock et al.,

under review) were used as non-priming control. Those sub-

jects participated in the saccade adaptation task but not in the

scrambled sentence task, were healthy, right-handed and 58.7 ±

4.4 years old.

Horizontal and vertical eye movements were registered by

electrooculography (DC-EOG) with a band pass filter of 0.08 -

100 Hz. Signals were digitized with a resolution of 0.01 deg/bit

and a sampling rate of 100 Hz, and calibration was repeated

every five episodes. Custom-designed interactive software de-

termined saccade direction as the angular difference between

first target step and primary saccade, in the plane of the screen.

The software also determined saccade latency as the delay be-

tween first target step and the onset of primary saccade. Sac-

cades with latencies beyond 270 ms were discarded, since they

may be influenced by reprogramming towards the second step

(Becker & Jürgens, 1979). Mean saccade directions for each

subject and episode were adjusted by subtracting the sub-

ject-specific baseline values before graphical presentation and

statistical analysis.

Results

Figure 1 illustrates that during the adaptation phase, saccade

Figure 1.

Saccade direction for each episode of the adaptation phase (25 episodes)

and the aftereffect phase (2 episodes). Means across subjects primed

with positive age stereotypes are shown in grey, those across subjects

primed with negative age stereotypes in black, and those across non-

primed control subjects are dashed. For better clarity, no error bars are

shown.

direction gradually increased towards the negative, as expected

for adequate adaptation. This increase was most pronounced in

the group primed with positive age stereotypes, reaching a

mean of −8.1 deg across the last five adaptation episodes. The

five-episode mean of saccade direction was only −4.7 deg in

the control group and −4.4 deg in the negatively primed group.

When a deviant, non-adapting subject was excluded (84% of

data from that subject were positive rather than negative), the

five-episode mean in the negatively primed group changed to

−5.6 deg. In fact, the deviant subject is excluded in Figure 1

and in the reported statistical analyses. The five-episode means

of saccade direction in all subjects were submitted to an

one-way analysis of variance (ANOVA) with the factor Group,

which yielded statistical significance (F(2,20) = 9.38; p =

0.0013). Fisher’s LSD post-hoc tests revealed significant dif-

ferences between positive and negative group (p < 0.01), be-

tween positive and control group (p < 0.001) but not between

negative and control group (p > 0.05).

Figure 1 further shows that saccade direction during the last

two (aftereffect) episodes was quite similar in all groups. Ac-

cordingly, when mean saccadic direction across both aftereffect

episodes was submitted to one-way ANOVA, no significance

was yielded (F(2,20) = 0.014; p > 0.05).

Discussion

The present study manipulated subjects’ performance th-

rough semantic priming. This technique is thought to activate a

specific node in a lexical network and thus to facilitate the sub-

sequent processing of words with similar meaning (Kiesel,

Kunde, & Hoffmann, 2007). However, it also was found to

influence higher-order mental functions such as creativity

(Mayer & Mussweiler, 2011), self-confidence (Levy, Hausdorff,

Hencke, & Wei, 2000), product preference (Strahan, Spencer,

& Zanna, 2002) attention focus (Hüttermann, Memmert, &

Bock, 2012) and motivation (Hart & Albarracín, 2009; Radel,

Sarrazin, Legrain, & Gobancé, 2009). We used this approach to

activate positive or negative age stereotypes in our subjects, and

observe the consequences on saccadic adaptation.

Our data document a beneficial influence of positive primes

on performance during the adaptation phase, but not during the

aftereffect phase. This suggests, according to established rea-

Open Access 1015

O. BOCK ET AL.

soning (Bock, 2005; McNay & Willingham, 1998), that posi-

tive age stereotypes enhanced workaround strategies but not

adaptive recalibration. Somewhat surprisingly, negative primes

had no noticeable effect at all: they modified neither recalibra-

tion nor strategies. One possible explanation is that priming

with negative age stereotypes is less efficient than priming with

positive ones. Another explanation could be social: maybe sub-

jects came to the laboratory already with a negative attitude

towards old age, and negative priming was therefore precluded

by a floor effect. There indeed exists empirical evidence that in

Bulgaria, compared e.g. to Germany, old age is regarded less

favorably. Bulgarians rate the social status and the economical

contribution of elderly persons much lower than Germans do,

and rate their own experience of discrimination due to old age

as much higher than Germans do (Abrams, Vauclair, & Swift,

2011). These findings might be related to the fact that suicide

rates among the elderly are substantially higher in Bulgaria than

in Germany (Shah, Bhat, McKenzie, & Koen, 2007). To decide

between the two explanations, it would be desirable to compare

the effects of positive versus negative age priming in different

cultures, including those who traditionally venerate their elders.

In this respect, it is interesting to note (Levy & Langer, 1994)

that memory loss in old age is more severe among Americans

with intact hearing than in American Deaf (who don’t experi-

ence spoken age stereotypes), and also more severe than in

mainland Chinese with intact hearing (who live in a culture that

honors old age).

The outcome of our study is in accordance with the hypothe-

sis stated in the Introduction section. Thus, the strategic contri-

bution towards saccadic adaptation might deteriorate in some

seniors more than in others, depending on their assimilation of

societal stereotypes, and only reaches statistical significance

when the role of stereotypes is controlled for by priming. This

could explain why no reliable deficit was observed when un-

primed older subjects were compared to young ones (Bock et

al., under review), but a robust deficit emerged when older

negatively primed subjects were compared to older positively

primed ones in the present study. In any case, age-related dec-

rements of saccadic adaptation, like those of arm adaptation

(Bock, 2005; Fernández-Ruiz et al., 2000; McNay & Willing-

ham, 1998), seem to afflict strategies but not recalibration. The

decrements seem to be less pronounced for the eyes than for the

arm, where a significant difference between age groups was

repeatedly observed even without primes (Bock, 2005;

Fernández-Ruiz et al., 2000; McNay & Willingham, 1998),

possibly because of a stronger cortical involvement in the con-

trol of arm versus eye movements.

Conclusion

The present study takes its place alongside other researches

that documented the role of social preconceptions on sensori-

motor performance (Hausdorff et al., 1999; Levy, 2000; Levy

& Leifheit-Limson, 2009), and thus highlights the potential

dangers of a vicious circle where negative attitudes towards old

age may activate performance deficits in the elderly by way of

self-fulfilling prophecy, which in turn enforces the negative

attitudes.

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