Implicit sequence learning in a joint action task

Psychologisch ontwerpen 2

Course number: 290201

Date: 23.01.2009

Abstract

This study was conducted to determine the difference in implicit learning between people who

were alone or in a social context. This was measured with a serial reaction time tasks (SRT) where the

participants had to react to two out of four different stimuli with their right or left hand. But what they

did not know is that the stimuli were part of a hidden sequence. Participants were either alone (single

condition) or together (joint condition). In both conditions a gradual increase in speed indicated that

both groups learned the sequence and that importantly there was a marginally significant difference

between how the two groups learned. Additionally, we found that participants in the joint condition

sitting on the right were faster with their right hand and participants sitting on the left side were faster

with their left hand. Post-hoc analysis showed that participants seated on the left were faster and error

rates of participants with their right hand were lower. In conclusion, the difference between singles

and joints seem minuscule but the effects of seating position are profound.

Key terms Implicit learning, Joint action, Sequence learning, SRT task

Ricarda Braukmann 0163066

Niels Lettinga 0151483

Dominic Portain 0163503

Jacek Sliwinski 0163619

Tutor: Jurjen van der Helden

University of Twente

Introduction

Making music in a band or playing ball with friends, are all very common and seemingly

simple actions we accommodate in our daily lives. Yet few of us think or even marvel about how such

a joint action is actually achieved and how it distinguishes from a task that we perform alone. There is

no doubt that our actions are influenced by social contexts, e.g. people often change their opinion

when confronted with social pressure (Asch, 1956). Zajonc (1965) described in his social facilitation

theory that the presence of others influences the performance respectively to its difficulty, where

subjects tend to perform better in simple tasks and worse in difficult tasks. Concerning our study, in

which participants had to react to symbols on a screen by pressing the correct button, social facilitation

predicts faster reactions if pressed during the presence of another person. Guerin (1993) attributed this

effect due to the change of arousal and social comparison. Assuming that two participants are sitting

next to each other performing an identical task, they tend to compete with each other for who will

perform better, which also tends to increase the state of arousal. Performance is predicted to increase

to a certain level of increased arousal, but decreases afterwards (Yerkes & Dodson, 1908). We did not

expect that the participants in our study to reach that peak or even go beyond it because the task was

not especially arousing for the participants. This encouraged our prediction that performance will be

enhanced. But in spite of being able to make a prediction how the social context influenced

performance in general, it is not quite clear how it affects learning in particular.

The focus of this study lies on a learning and memory conceptualization that is known as the

procedural or implicit system (Ashby & Ell, 2002; Squire, 1994), which appeals to a passive process

of skill or information acquiring simply through exposure while unable to recall. This means that

people learn although they are often not consciously aware of it. Just think of dancing. It is hard to

explain when and where to execute a step, but with practice you will get a kind of feeling for it. To

examine implicit learning in our study we made use of a serial reaction time task (Nissen & Bullemer,

1987). Participants had to react to different stimuli appearing on a screen. In our case one of four

symbols were shown and the participants had to react by pressing the correct button. For the simple

reason that responding occurred to one stimulus at a time, it became a Go/NoGo task. What the

participants did not know is that there was a hidden sequence, a certain order of symbols. This is our

learning sequence which we expected participants to learn. This will be measured by observing the

reaction times through the repeated exposure of the sequence. We expected that learning will be

implicit because they will not be conscious aware of the sequence’s existence. To determine the extent 2

of implicit or explicit learning we used in addition to reaction times a recognition task, which was also

used in prior studies (Willingham, Greeley & Bardone, 1993; Bird, Osman, Saggerson & Heyes,

2005). On the recognition task three symbols were shown at a time, they were either fragments of the

learning sequence or random stimuli, the participants were asked how familiar they seem to them.

That means that if the reaction times would be faster to fragments of the learning sequence, but they

are not evaluated as being more familiar, it indicated that the participant learned the sequence

implicitly. This means that they are not consciously aware of the hidden learning sequence.

H1: During the recognition task, parts of the sequence will be better recognized than random stimuli.

After having evaluated the method for determining the amount of implicit learning, the next

step was to determine if there was a difference in learning between a participant performing the task

alone or with another participant. Acting in a social context is different from acting alone. Participants

who performed the task alone are from now on called to perform in a “single condition” and those who

accomplished the task together are called to be in a “joint condition”. As a definition of joint action we

adopted the view of Sebanz, Bekkering & Knoblich (2006) who described it as a form of social

interaction comprising at least two individuals coordinating their actions in space and time to achieve

a goal by manipulating their environment. Its success depends on the abilities to share representations,

predict actions and integrate predicted effects of one’s own and other’s actions. The term shared

representations could be described as a mutual understanding of the perceived environment and the

goals of a task. In our case the shared representation of the participants in the joint condition consisted

of the control of the buttons and the goal to press them when the correct stimuli appeared on the

screen. The success depended on the right prediction not only when to press their own buttons but also

to predict when the other participant has to press their buttons, thereby improving the prediction of

when to press their own buttons. A series of studies by Knoblich & Jordan (2002, 2003) showed that

an unambiguous feedback about each other’s timing of action planning is crucial for an effective

anticipatory action control and can be as important as internal signals. This emphasized the importance

of a reliable prediction of what the joint effects of one own and another participant’s actions would be.

We expected that this effect would become visible in a reduction of reaction times during the learning

sequences.

H2: In the joint condition, participants will learn faster than in the single condition.

Recent studies showed that the forming of shared representations happened automatically,

even if it would be more effective to ignore one another (Sebanz, Knoblich & Prinz, 2003; Sebanz,

Knoblich, Stumpf & Prinz, 2005; Atmaca et al., 2005 in Sebanz, Bekkering & Knoblich, 2006). This

phenomenon is explained by the assumption that observing an event that regularly results from one’s

own actions induced the tendency to carry out this action. For example, not only the participants in the

joint condition but also the investigator who is present to observe the participants would share the

3

common representation, although not intentionally. Consequently, perceiving actions of others should

activate the same representational structures that manage one’s own planning and control of these

actions. The simulation theory (Gallese & Goldman, 1999) explained that the capability to predict

actions of others relied on the ability to simulate their actions because it relied on the same brain

regions. According to Gallese (2006) and Newman-Norlund, van Schie, van Zuijlen & Bekkering

(2007) these brain regions are called the human mirror neuron system. Cells in the mirror system fire

not only if an individual performs an action, but also if the same action is being observed. Accordingly

the cells in the mirror system will not only fire in the participant who is pressing a button but also in

the other participant in the joint condition.

Tsai, Kuo, Jing, Hung & Tzeng (2006) constructed a study concerning joint action quite

similar to this one. He used a Go/NoGo task in three different conditions to determine the influence of

social interaction. There are two main differences comparing this study to Tsai, et al. (2006). First, in

the experiment of Tsai, et al. (2006) there were only two types of different stimuli compared to the

four types in this study. Second, the stimuli were presented with equal possibility in three spatial

positions, left, middle and right, in this study stimuli were only presented in the center. In Tsai, et al.

(2006) reaction times of the middle stimuli were taken as a baseline to be subtracted from the reaction

times of compatible and incompatible trials. In a compatible trial the spatial relationship between

stimulus and response is correspondent, thus when the target stimulus appears on the same side as the

response, hence the responding participant. In incompatible trials in contrast the spatial relationship

between stimulus and response is non-correspondent, thus when the target stimulus appears on the

opposite side as the response, hence the non-responding participant. This spatial stimulus-response

compatibility is also known as the Simon-effect. Simon (1969) found that people react faster and more

accurate when a stimulus appears in the same relative location as the response. He attributes this effect

to an innate tendency to respond towards the source of the stimulus. Regarding the study of Tsai, et al.

(2006) results showed that compatible trials do have significant faster reaction times than incompatible

trials, which leads us to our third hypothesis.

H3: The reaction times will be faster when the location of the participant is the same as that of the

button that has to be pressed.

4

Method

Participants

45 healthy volunteers (40 female and 5 male; mean age 20; range 18-27 years) with normal or

corrected to normal vision were tested after having signed a written informed consent. Participants

were tested for hand preference; all but one were right-handed. This experiment was approved by the

local ethics committee.

Stimuli and Reaction

A black screen was presented for 1500ms. Afterwards, one of four stimuli (square, circle, star

and triangle) was presented in the middle of the screen. Each symbol had a width of 20 mm and was

presented on a 17’’ CRT computer screen. The stimuli were presented maximally for 1000 ms or until

the correct response was given. The PC connected to the response boxes recorded all button timings

together with the stimulus data. Participants were seated in a viewing distance of approximately 65

cm, which resulted in the stimuli to cover 1.7 degrees of the visual field. Participants were told to react

as quickly as possible, and to minimize error rates.

Participants had to react to different stimuli with their left or right hand. When a circle

appeared the participant seated on the left had to press the left button on a response box. The correct

response for when a star appeared was for the participant sitting on the left to press the right button on

the response box. Accordingly, the participant seated on the right had to press the left button when a

square appeared and the right button when a triangle appeared. Custom response boxes were labeled

with drawings of the stimuli next to the according buttons. All of the labels were approximately 4 cm.

The response box on the left seat position showed a circle label on the right side of the left button and

a star label on the left side of the right button. This label showed a five-sided star instead of a four-

sided star, as used as stimulus. On the right seat position, the response box showed a square label on

the right side of the left button, and a triangle label on the left side of the right button. The buttons for

the left response box were colored red; those for the right response box were colored green (see figure

1). These boxes were connected to the computer via the parallel port. The PC connected to the

response boxes recorded all button presses together with the stimulus data.

Figure 1. This figure shows the boxes for the participants. The left box was for the participant sitting on the left and the right box was for the

participant sitting on the right.

For preparation, participants practiced the response with a small block of eight random items.

In general, the following conditions counted as procedural errors: pressing the wrong button, reacting

when no response was needed, and missing the response item longer than the reaction time of 1000

ms. In case of the wrong reaction, the current symbol remained on screen until the right button was

pressed or the reaction time passed. The practice block was rehearsed until the performance was

acceptable, then the procedure continued to the learning task. The stimuli during the learning blocks

were part of a 12-item second-order conditional (SOC) sequence. This led to a smallest learning block

of three subsequent stimuli, whereas the first two stimuli had to be sufficient and exclusive to predict

the third one. Due to the second-order conditional sequence, two succeeding stimuli could not be the

same (e.g. after a circle a different stimulus had to appeared). Different symbols were equally

distributed between participants, where repetitions and reversals were prevented as much as possible

to account for inhibition of return. However, a sequence of 12 symbols has to include at least one

reversal – at this point at the▲▲ part. Each learning block was started with four randomly chosen

stimuli to prevent sequence recognition during the beginning of all subsequent blocks. Each one of the

eight blocks showed ten repetitions of the symbol sequence, resulting in 120 + 4 symbols per block. At

the end of each block, the number of errors was shown during a short pause of ten seconds. The

learning task provided the basis for implicit learning. The symbol sequence during this part was shown

as can be seen in figure 2.

Figure 2. This figure shows the order of the sequence during the first 8 blocks. The participants on the left had to press with their left hand

when a star appeared and with their right hand when a circle appeared. The participants on the right had to press with their left hand when a

square appeared and with their right hand when a triangle appeared.

After the eight learning blocks, two varied blocks of similar length followed. After each

varied block, one block with the original sequence was inserted to provide a reference of measure.

First, a “Switch” block (9th block) was presented, where reaction between the left and right hand was

switched (see figure 3). This means that the order in which the stimuli appeared changes. Where in the

original sequence a star appeared there would now be a circle and when a circle appeared there would

now be a star. This was the same for triangles and squares. Where in the original sequence a triangle

appeared there would now be a square and when a square appeared there would now be a triangle.

Figure 3. This figure shows the order of the sequence during the Switch block. The participants on the left had to press with their left hand

when a star appeared and with their right hand when a circle appeared. The participants on the right had to press with their left hand when a

square appeared and with their right hand when a triangle appeared.

To pose a reference to the “Switch” condition and to indicate how strong the change from

learning to varied blocks would be in general, a “Random” block (11 th block) was inserted. In this

block, 124 symbols appeared in a pseudorandom manner (corrected for repetitions and reversals,

evenly weighted between participants).

Group conditions

All experiments were split into two different conditions. First, the “joint” condition included

two participants sitting in front of one monitor. To prevent communication between participants,

especially hints about the sequence, one research assistant was seated in the same room. Participants

were subsequently asked not to talk or to ask questions during the test. The research assistant was very

quiet and did not move to prevent a possible influence. The “single” condition included only one

participant, seated on either the left or right chair. The response task for participant in the single

condition was identical to the joint condition. To provide an equivalent task environment as that of the

joint condition, the appropriate responses from the missing partner were provided by a computer

program. The otherwise naturally occurring variances of the test partner, including RT decline, were

hereby simulated by a prerecorded and statistically cleansed series of reaction times. All experiments

took place in a quiet room with constant light conditions. All environmental variables, including the

research assistant, remained constant over all trials and both conditions.

Analysis

We used repeated measured ANOVA to analyze our data. Therefore we had to take the

Mauchlys sphericity test into account. We used the Greenhouse-Geisser adjusted p value if the

significance level of Mauchlys test was lower than .05. However we still report the original degrees of

freedom. We analyzed with Block and Button as within-subject variables and Group and Position as

between-subject variables.

Results

Block 1 to 8

First, we considered the learning effect of our experiment. This effect can be seen through the

change in reaction times and errors during the different blocks. Figure 4 shows these changes for the

two different groups. A gradual decrease in reaction time could be observed during the learning phase

which includes Block one to eight (F (7,36)= 4.9, p < 0.001). This indicated that participants learned

the sequence during the first eight blocks. Consistently there was also a gradual decrease in errors

during this learning phase (F (7, 36) = 5.2, p < 0.001).

Figure 4a. This figure shows the reaction times for the different

blocks separated for the “joint” and the “single” group. In this

figure, 1 stands for the single condition and 2 stands for the joint

condition. On the x-axis the different blocks of our experiment can

be seen. On the y-axis you can see the reaction times of the

participants given in milliseconds. In block 1 to 8, block 10 and

block 12 the participants had to react to the normal sequence, block

9 is the “Switch” block and block 11 is the “Random” block.

Figure 4b. This figure shows the errors made in the different

blocks. On the x-axis you see the different blocks of our

experiment. On the y-axis the errors made by the participants are

shown. In block 1 to 8, block 10 and block 12 the participants had

to react to the sequence, block 9 is the “Switch” block and block 11

is the “Random” block.

Because we hypothesized that the learning effect of the first eight blocks would be different

for the two groups, we expected an interaction between this Block-effect and Group. We found that

this effect was marginally significant (F (7, 36) = 1.8, p = 0.097). This confirmed our expectation that

participants in a “joint” condition learn in a different way than do participants in a “single” condition.

We expected that there would be a comparable effect in the errors the participants made. This was not

confirmed (F (7, 36) = 0.72, p = 0.621). Therefore the change in reaction time differed in the “joint”

and the “single” condition but the errors the participants made did not. Concerning the social

facilitation theory and the studies about shared representations we would expect the participants in the

“joint” condition to react faster. As figure 4 shows, the differences between the two lines of reaction

time did not vary that much and even the “singles” seemed to react faster than the participants in the

“joint” condition. The greatest difference can be observed in the first two blocks. Therefore our second

hypothesis is not confirmed.

Besides these learning effects we expected an interaction effect of the seating position and the

button the participants had to press. This suggestion was confirmed by our findings for the reaction

times (F (1, 36) = 20.3, p < 0.001). The participants sitting on the right side were faster with their right

hand. The participants sitting on the left side were faster with their left hand. This is shown in Figure

5. Hereby confirming our third hypothesis. Additionally, we found an interaction effect between

Button and Position with the error findings (F (1, 36) = 4.1, p = 0.05). Comparable effects were also

found in other studies. For example, the experiment of Tsai (2006) indicated that there is a relationship

between the seating position of the participants and their reaction times.

Figure 5. This figure shows the interaction effect between the seating position of the participant and the button that had to be pressed. In this

figure, Button 1 stands for the left button and Button 2 stands for the right button. The x-axis describes the position of the participant and on

the y-axis you can see the reaction times of the participants in milliseconds. The person sitting on the right was significantly faster with his

right hand, the left participant with his left hand.

Besides these expected effects we found two other main effects and three other interaction

effects. The most important additional effect we found was the interaction effect between Button,

Position and Group (F (1, 36) = 5.2, p = 0.028). This effect can be found in Figure 6a and 6b. Because

we generally expected differences between the “joint” and “single” group we analyzed the Button-

Position effect for both groups separately. We found that the interaction effect was only significant in

the “joint” condition (F (1, 18) = 67.6, p < 0.001) but not in the “single” condition (F (1,18)= 1.481, p

= 0.239). This indicated that in the “joint” condition the difference between the reaction times of the

left and right button is greater for the participant sitting on the right. We also found this interaction

effect in the errors results. The difference between the errors on the left and right button is greater for

the participants sitting on the right than on the left side. Through further analysis we found that this

effect was only significant for the “single” condition (F (1, 36) = 5.1, p = 0.03).

Figure 6a. This figure shows the interaction effect between Button

Position in the” single” group. In this figure, Button 1 stands for the

left button and Button 2 stands for the right button. On the x-axis

you see the seating position of the participants and on the y-axis

their reaction times in milliseconds are shown. The fact that the two

lines are quite identically indicates that the effect is not significant

in this group which was confirmed through analysis.

Figure 6b. This figure shows the interaction effect between Button

and Position for the “joint” group. In this figure, Button 1 stands for

the left button and Button 2 stands for the right button. On the x-

axis you see the position of the participants and on the y-axis the

reaction times in milliseconds are shown. In comparison with figure

7a you can see that the lines differ from each other. Consistently we

found that the effect was significant in this group.

The first main effect we additionally found was the effect of Position with the reaction times.

The participants seated on the left position reacted significantly faster than the participants on the right

position (F (1, 36) = 5.7, p = 0.022). This effect was found during the entire experiment and was

significant for both groups. There are several explanations for these findings. On the one hand this

effect could be explained by the seating location, indicating the importance of where a participant is

seated. On the other hand this could be an effect of the structure of the sequence, which is different for

the participants. There was no such effect found with the errors.

The second main effect we found was the effect of the Button with the errors (F (1, 36) = 9.3,

p = 0.004). If participants had to press the right button they made fewer errors than if they had to press

the left button. There are several explanations for this finding. This effect might be caused either by

the structure of the sequence or because of the fact that all but one participant were right handed.

Additionally, we found a moderately interaction effect between Button, Block and Group (F

(7, 36) = 1.9, p = 0.077). This was only significant in the “single” condition (F (7, 18) = 3.0, p =

0.006). We also found an interaction effect between Button, Block, Position and Group (F (7, 36) =

2.1, p = 0.046) in the errors. Through further analyses this effect was not found to be significant for

any of the two groups. We assume that this could have been caused by some factor but that it does not

have a relevant influence on our experiment. Finally, we found an interaction effect between Button

and Block in the errors (F (7, 36) = 2.2, p = 0.035).

Switch-Block effects

First we found a main effect of the “Switch” block (F (3, 36) = 18.8, p < 0.001). We found a

difference in the reaction times between the “Switch” block and the flanking blocks of the “Switch”

block. The participants were slower reacting to the switched stimuli. We also found this main effect in

the results of the errors (F (3, 36) = 4.02, p = 0.015). The participants significantly made more errors

in the “Switch” block which indicates learning.

The second main effect we found was an effect of Position with the reaction times (F (1, 36) =

9.4, p = 0.004). Similar to the Block effects we found that the person sitting on the left was faster. It is

likely that this was caused by the same factors that we mentioned above in the paragraph about Block.

Finally, we found an interaction effect between Position and the “Switch” block (F (3, 36) =

16.2, p < 0.001). The difference between the left and right “Switch” was greater for the participants

sitting on the right than on the left. Further there were no effects of Group or Button found for the

“Switch” block.

Random-Block effects

The difference in the reaction times between the “Random” block and the two flanking blocks

of the “Random” block was significant (F (3, 36) = 19.6, p < 0.001) and on the errors (F (3, 36) = 3.9,

p = 0.019). This confirms our hypothesis that the participants learned during the experiment.

We also found a main effect of Position (F (1, 36) = 7.9, p = 0.008). Again the participant

sitting on the left sight reacts faster than the person on the right.

Additionally we found an interaction effect between “Random” and Position (F (3, 36) = 5.2,

p = 0.009). The difference between the left and right “Random” was greater for the participants sitting

on the right than on the left.

Finally, we found a moderately significant interaction effect between Position and Group (F

(1, 36) = 3.8, p = 0.06). Because we generally expected differences between the “single” and the

“joint” condition we will discuss this further. Through further analysis we found that the effect was

significant in the “single” condition (F (1, 18) =9.1, p = 0.07), but not in the “joint” condition. In the

“single” condition, the participants sitting on the right were significantly slower.

Difference between Switch-Condition and Random- Condition

We used the “Switch” block to determine how the participants learned and what it is that they

exactly learn. Therefore a difference between the “Random” and the “Switch” would indicate that

participants had learned when to react because in the “Switch” block the moment of reaction stayed

the same for the participants only the button they had to press changed. This was not confirmed in our

analysis. We found no significant difference between “Switch” and “Random” in either the reaction

times (t (39) = 1.356, p = 0.183) or the errors (t (40) = -1.388, p = 0.173). This indicates that the

participants did not learn a fixed scheme of responses, but reacted according to the stimuli.

Discussion

The main focus of this study was to investigate the difference in learning alone and learning

together with someone, a so called joint action. Comparing the participants in the “joint” and the

“single” group, we found that the participants did learn in a different manner, although the difference

was only marginally significant. We expected that people in the “joint” condition reacted faster

according to earlier evidence from social facilitation theory. The difference we found can mainly be

attributed to the first two of the eight blocks where the “singles” reacted faster than the “joints”. The

overall differences presented in Figure 4 seemed not significant because the two lines representing the

reaction times of both groups are quite similar. Furthermore, the fact that the “singles” were faster than

the “joints” leads us to reject our hypothesis. Because our findings are only marginally significant we

are inclined not to state that there are important differences between participants in the” joint” and

“single” condition regarding the reaction times. This means that the process of learning is similar

when learning alone or learning together with someone.

Another point in our experiment was to test in what way participants learned. Therefore we

integrated the “Random” and the “Switch” block. We found no differences between these two blocks.

A difference between the “Random” and the “Switch” blocks would have indicated that participants

had learned a fixed scheme of responses. In the “Switch” block the moment of reaction stayed the

same for the participants, only the button they had to press had changed in respect to the prior

sequence. We initially intended to include another sequence to measure the extend in which the

participant learned not only when to push their own buttons, but also when the other participant had to

push their buttons. This could be achieved if the participant reacted on the instant when the other

participant had to react in the actual sequence. However, swapping the stimuli that had to be

responded to by pushing a button on the right box with the left would have resulted in an exact copy of

the original sequence, only shifted in time. Therefore, we did not include this sequence. For further

experiments, we suggest that this sequence should be included in the experiment. Comparing the

“Switch”, “Random” and the swapped sequence could indicate about how people learn and what they

actually remember. This design could help to determine if participants do only learn “their” moment of

response, or also the turns of their hands. It could even be possible they learned the reaction part of

their partner.

The second major finding of this experiment was the interaction of (seat) Position and Button,

which indicated that the participants sitting on the right were faster with their right hand and the

participants sitting on the left was faster with their left hand. These findings confirm our hypothesis

that reaction times will be faster when the location of the participant is the same as that of the button

that has to be pressed. This effect is quite similar to the effect found by Simon (1969). It is also

comparable to the study of Tsai, Kuo, Jing, Hung & Tzeng (2006) which is described in the

introduction. The difference between the two groups concerning the interaction between Position and

Button was not expected. We found that this effect was only significant for the participants in the

“joint” condition. This indicates that, in the “joint” condition, the difference between the reaction

times of the left and right button is greater for the participant sitting on the right. This could be

attributed to the sequence which was different for the participants depending on the seat position, but

that would not explain the absent significance for the “single” group. Another explanation could be the

presence of the investigator, who was positioned on the left side in all the experiments and could have

had a social influence on the participants. Again, this is not an adequate explanation, because this

effect was not found in the “single” condition. These are mere suggestions, and more evidence is

needed to make confident conclusions about the origin of this effect.

Further post-hoc analysis showed that participants who were positioned on the left side were

faster than participants who were positioned on the right side. This was found for both the single and

the joint group. The influence of Position could be explained by two factors. First, the sequence might

be harder for the person on the right. In our sequence, the participant sitting on the right had to react to

a specific stimulus (▲). After that, the other participant had to give a response. Then, the participant

on the right had to press the same button (▲) again. This was not the case for the participant sitting on

the left. We assume that this property of the sequence could have made it harder for the person sitting

on the right. The related phenomenon “inhibition of return” states that it is harder for people to react to

a stimulus at a specific location where another (or the same) stimulus just appeared, than to react to a

stimulus where no stimuli were shown recently (Posner, Rafal, Chaote and Vaughn, 1985). Second,

the presence of the investigator might have had a social influence on reaction times. Abrahamse, van

der Lubbe and Verwey (2007) also found an influence of the investigator presence on the reaction

times of their participants. They found that the reaction times decreased when the investigator walked

into the room. Although this is not comparable to our study, it suggests the high influence an

investigator can have on the participants.

Post hoc analysis also showed that if participants had to press the right button, they made

fewer errors than if they had to press the left button. There are several explanations for this finding.

First, the effect might be caused either by the structure of the sequence comparable to the effect of the

position that we just described. Second, all of the participants but one were right handed. Because they

were right handed, they probably had better movement control over the right hands and therefore were

prone to make less errors with that hand. This were the main findings concerning the two groups their

position and the button they had to press.

Our experiment was concerned with implicit learning. Because of an unexpected loss of the

recognition task data, we are unable to determine whether the participants learned implicitly or

explicitly. This leaves our first hypothesis unanswered.

Further, as already mentioned, the investigator was always positioned on the left side during

the experiment. Therefore, we are not able to determine the influence the investigator had on both the

participants. For following studies, we suggest that the investigator should be positioned on the left

and right sides equally. For this study, the presence of an investigator during the experiment was

necessary, but maybe following studies can be constructed in a different way.

Another point of discussion is that the participants were able to choose their time of

participation. Therefore, it was possible for friends to take part in the experiment together. The

familiarity, or unfamiliarity, between the participants might have influenced their behavior. We

suggest that following studies randomly assign participants to single and joint conditions.

Practical implications

In this section, we would like to discuss the practical use of the findings from this study. We

will first take a look at implicit learning in the single as well as the joint condition and after that, we

will discuss the utilization of the Simon-effect.

The first finding could be meaningful for an educational setting. Implicit learning has always

been a feature of the nurture of children, just think of teaching facts to children like numbers or

moving patterns by simply playing with them. In an advanced age, this process could be used for

exercising mathematics, such as algorithms and other logical constructs of numbers. The mere

exposure to them could provide a support to solve later mathematical problems.

Implicit learning is also a main feature of sport, regarding again the prior example of dancing.

It is not possible to teach somebody to dance by explaining it to them – this has to happen during the

process. Regarding our results, we can conclude that dancing is learned in a different manner if

exercised with somebody else (e.g. ballroom dance) than alone (e.g. ballet). According to our findings,

we would expect that singles learn faster than couples, at least in the beginning. Our recommendation

is therefore to always learn alone during the early stages of acquiring difficult movement patterns.

The second finding could be of great importance in the area of ergonomics. Keeping in mind

the position of the instruments and the user, ergonomists can render the design of product more usable.

The range of applications is huge, but the importance of reaction times is the most relevant for safety

appliances like the cockpit of an airplane. For example, if the captain of a plane is sitting on the right

side, most of the critical buttons should also be located on the right side. Through carefully structuring

and positioning the instruments in this respect, reaction times could be decreased permanently. And in

some situations, even a small improvement of reaction time can be of crucial importance.

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