Biological practical reported

The localisation of brain function

This is to be used as a source of background information and a guide for what to put in each section of the practical report. You must not copy materials directly from here , and you should use your own words to construct a flowing argument for why the research is being conducted.

General topic area: brain lateralisation/hemispherical specialisation, handedness and language production


The purpose of this practical was to investigate a topic relevant to biological psychology, or more specifically neuropsychology. Neuropsychology is the study of the ways in which the physical structure of the brain are related to behaviour.

Various techniques are available for the study of brain structure and function. These include lesion studies in which the effects of brain damage are investigated and electrical stimulation of the brain. In transcranial magnetic stimulation (TMI) an intense magnetic field is applied to part of the brain to temporarily interfere with its function. More recently brain imaging techniques such as positron emission tomography and functional magnetic resonance imaging (fMRI) have enabled us to look at the amount and location of brain activity associated with different tasks. 

This practical was concerned with the consequences of two fairly robust findings from previous work. While the relationship between the structure and function of the brain is an interesting topic in its own right, it would be particularly interesting for psychologists if the findings have behavioural implications i.e. as a result of brain organisation, the performance of certain tasks or combinations of tasks is helped or hindered. 

The first of the findings that we will consider is as follows:

The brain consists of two halves: the cerebral hemispheres. One function of these is the control of body movement. It has been found that each hemisphere is responsible for controlling the movement of the opposite (contralateral) side of the body. Thus, for example, movements by your right hand and arm are controlled by your left cerebral hemisphere, while movements by your left hand and arm are controlled by your right cerebral hemisphere.

The second of the findings that we will be considering is as follows:

For right handers, it has been found that there is a strong tendency for language functions to be located in the left cerebral hemisphere. This is particularly the case for speech production. Two distinct areas have been identified: Wernicke’s area (located just behind top of the left ear) appears to be responsible for comprehension of spoken language and for producing meaningful strings of words. These word strings are then transmitted to Broca’s area (located just in front of the left ear, slightly above the level of Wernicke’s area) which appears to be responsible for producing the muscle movements associated with pronouncing word sounds. It is very rare indeed for equivalent highly specialised speech centres to be found in the right hemisphere.

What could be the consequences of such an arrangement? We know that people often experience difficulty when they are given two novel tasks to perform concurrently (the issue becomes less clear when one or both tasks become highly practiced or automated). This implies that the brain has limited resources and that novel tasks must compete for these resources with the result that the performance of one or both may suffer. What would we expect if a person had to perform a difficult verbal task, and at the same time had to perform a difficult motor (manual) task with the right or left hand?

When the verbal task is being performed concurrently with the left hand manual task, opposite hemispheres are active (left hemisphere verbal task, right hemisphere manual task). This means that the tasks are likely not to be in competition for the same resources and performance at the manual task while verbalising should be little different from performance at the manual task without verbalising.

When the verbal task is being performed concurrently with the right hand manual task, the left hemisphere is required for both tasks. This means that the tasks may be in competition for the same resources and performance at the manual task while verbalising will be worse than performance at the manual task without verbalising.

Diagram  Description automatically generated

N.B.  we are not interested in directly comparing right hand performance with left hand performance. The right hand will probably always (for right handers) out-perform the left hand on any given set of tasks. We would also expect the performance when silent to be better than when speaking. Instead we will be looking at the performance of each hand separately, with and without verbalising and comparing the size of the decrease in performance.

An experiment like this was first performed by Kinsbourne and Cook (1971) who asked participants to balance a rod on one finger while performing a verbal task, and did find that as predicted, participants did worst when balancing the rod on the right hand and speaking at the same time.  Since then researchers have carried out a variety of experiments along these lines, using varying tasks, to measure the strength of the effect depending on the type of tasks, participants, and amount of practice.  A number of explanations have been put forward, such as Kinsbourne and coauthors’ reference to ‘functional space’ and the statistical bias hypothesis: you should consider and critically evaluate at least two explanations for the findings.

In our experiment new tasks were devised to add to the empirical findings on the topic, which are mostly quite old with small numbers of participants.  The manual task used in our experiment involved tapping a moving target on the computer screen with the mouse pointer as quickly and accurately as possible, using the left or right hand to control the mouse and clicking the mouse button with the left or right index finger to tap the object. The verbal task consisted of saying the alphabet with examples (e.g. “A is for apple, B is for bear, C is for catamaran….”) while performing the tapping task.

The Experiment

First year undergraduate psychology students at the seychille university  performed this experiment.  They each undertook the experiment individually. Data will be kept separate for right handed and left handed participants. Left handers are taken to be those who prefer to write with the left hand or have no particular preferred hand for writing. There are more complicated ways of assessing handedness but we will not be concerned with these.  The hemispheric organisation of left handers is more complicated than for right handers (at least with respect to language) so we collected but will not analyse the data for left handed participants.

Each person had access to one of the PCs and a list of sentences. On the computers they ran a custom-built movement task which could be performed with either the left or right hand.  It used a within-subjects design (each participant completed all four conditions). They started with a practice phase.  The practice phase is necessary otherwise there would be a steady improvement in tapping ability while the experiment was taking place. This would add ‘noise’ to the data, making the effects that we are looking for harder to find. For the practice phase they performed the tapping task twice with each hand, in silence. After the 30 seconds, they took a rest for about 30 seconds before using the other hand to practice for another 30 seconds. They repeated this a second time, so they had 2 minutes practice (1 minute per hand). 

For the experimental phase they worked individually and at their own pace. There were four different conditions (SL – Silent Left hand,  SR – Silent Right hand, VL – Vocal Left hand and VR – Vocal Right hand). They completed 3 tries in each condition – a total of 12 trials in all. For counterbalancing they were given a number from 1-4 and performed the trials in the following order:

Group / Trial123456789101112

Performing the trials in this way ensures that the overall frequency of each trial is the same at each position and all transitions are at equal frequency (this is similar to a Latin Square design so you could just say that a Latin Square design was used for counterbalancing). Participants rested for about 30 seconds between trials to prevent fatigue developing over the course of the experiment and introducing “noise” into the data.

For the verbalisation trials they first started repeating the alphabet with examples as explained above. When they finished a verbalisation trial they made a note of which letter they had reached and they started from that letter for the next verbalization trial. When they reached the end of the alphabet they went back to the beginning. For non-verbalisation trials, the procedure is the same as before except that they did the tapping task while silent.

At the end of each trial they wrote down their results from the summary screen onto the data collection sheet. This recorded the correct tapping rate (in taps/second).  When they had completed all the trials, they calculated their mean correct tapping rate in each of the four conditions.  Then they calculated the following columns, which you will find in the data file:

  • Mean tapping rate for the right hand
  • Mean tapping rate for the left hand
  • Mean tapping rate when speaking (=vocal/verbal condition)
  • Mean tapping rate when silent
  • For the right hand: tapping rate difference (calculated by subtracting the vocal tapping rate from the silent rate for the right hand)
  • For the left hand: tapping rate difference (calculated by subtracting the vocal rate from the silent rate for the left hand)

Writing the abstract

Although this section comes first, after the title page, you actually write the abstract after you have finished the rest of the report, as the abstract acts as a summary of it.

Writing the Introduction

Report will need to include:

  • Cortical organisation (for a brief introduction see Martin & Carlson “Organisation of the cerebral cortex” (p. 135-143).
  • Handedness (for a brief introduction see Martin & Carlson (p. 408-9).
  • Lateralisation of language function
  • At least two possible explanations proposed for the interference effect found by Kinsbourne and Cook and other authors.

This needs to make up the majority of the introduction

You need to present this information so that it makes a coherent story and not just as a list of facts

What can we predict?  Remember all participants must be right-handed. 

Likely to be a bit slower when tapping with the left hand than the right (dominant hand). 

Likely to be a bit slower tapping when speaking than when silent (because two tasks take more attention than one).

But how will tapping and talking interfere?  What can we predict?

When tapping with left hand, shouldn’t be any interference, as left hand controlled by right brain, but language in left brain, so tapping speed should be fairly similar whether silent or speaking

When using the right hand, expect interference as both using functions which are close by in the same hemisphere, so predict that tapping speed should drop down a lot in the speaking condition compared with the silent

So for right handed participants the DIFFERENCE in tapping rates between silent and speaking will be greater in the right hand than the left hand.

This is the point of the practical.  This hypothesis is the one that will only be true IF our ideas about cortical interference AND the location of the speech centres in right handers are correct.

The whole of your report should be built around this idea.

So you should have three hypotheses

  • Right handed participants will tap faster with their right hand than with their left  (regardless of vocal/silent condition)
  • Right handed participants will tap faster when silent than when speaking.  (regardless of hand)
  • For right handed participants the DIFFERENCE in tapping rates between silent and speaking will be greater in the right hand than the left hand.

Writing the Method section

Information for writing the participants subsection can be found here (type and motivation of participants) and in the data file (age and sex).  Mention that all participants were right-handed, and only give age/sex information for the right-handers.

Materials/apparatus – you just need to describe that a computer and computerised tapping task were used, and give a rough outline of what the tapping task involved.  The experiment took place in a university computer room i.e. standard Windows PC and mouse.  The software was a custom written tapping program (written in the School of Psychology)

Design –

We are manipulating IVs to test for differences, so this is an experiment.

What is / are our INDEPENDENT VARIABLES? i.e. What are we manipulating?

  • Which hand we use
  • What vocal condition we are in


  • Correct tapping speed (taps/second)

So what level of measurement is this? 

What SORT of experiment is it?  Within subjects or between subjects?

Each person does 4 things:

  • Right hand silent
    • Right hand speaking
    • Left hand silent
    • Left hand speaking

What is the problem with this?

Order Effects and Counterbalancing

If we did it in the same order then we might have problems due to:

  • Fatigue
  • Practice
  • Boredom

We get round this by counterbalancing as mentioned earlier

So, to summarise


We have 2 I.V.s and 1 D.V.


We COUNTERBALANCED using a Latin Square

Procedure – see this document earlier on

Writing the Results section

Start with a sentence explaining the scoring (mean tapping rate).  Assume the data is parametric (you don’t need to test assumptions).  Start by producing three graphs, one for each hypothesis, one contrasting the mean correct tapping rate for each hand, one contrasting the mean tapping rate for silence vs. speaking, and one to contrast the differences between silence and speaking for each hand.  After each graph you should carry out an inferential test – in this case you will be doing a t-test for each hypothesis.  This is because for each hypothesis you are comparing two means (normally this type of design would be tested using factorial ANOVA, but the way the data was collected this option is not available to us, so we have to use t-tests).

The data is in the file “SPSS data file”. Download it into SPSS or JASP, open it up and take a look.

1. The first task is to check you know what data is in which column and what the labels mean. For the handedness column I have used the “Value” field to set 1 = Right handed and 2 = Left handed.

2. Are we analysing all the data?

NO – we want to analyse the right handed data but not the left. We could just delete the left handers data but there are better ways to do this.

In SPSS use the “Select Cases” function. To do this go to Data…Select Cases… and in the resulting dialog box click select “If condition is satisfied” as shown below. In the resulting dialog box we want to make it look like the 2nd image below – by saying “If handedness = 1” this will tell SPSS to only analyse the right handed participants data. If you click OK enough times to close all dialog boxes and look at the data file you will see that SPSS has put a line through the left handed participants data and will not analyse it. If we later wanted to look at the left handed participants we would just reverse this process.

First Dialog box – activate “If…”Now move ‘handedness’ across and select = 1
SPSS puts a line through left handed people and will not include that data in the analysis

In JASP: Click on the Handedness column title to open the filter:

Graphical user interface, application  Description automatically generated

Then click on the tick next to label ‘left’ to turn it into a cross.  This filters out the left-handed participants.

Table  Description automatically generated

3. The next thing to do is to get some basic descriptive statistics to find out how many right-handed participants there are and to collect age and gender information for the participants section of the report.  For this and the rest of the analysis you have the teaching materials from the module, for example the step-by-step guides from the Introduction ones onwards: you have practised doing this previously and may need to return to revise the material first and work through the lecture examples before you can apply it to this new data set.

4. Then we need to make some graphs to illustrate our results.

We need 3 graphs – one for each hypothesis. In general the most appropriate graph for parametric data is an error bar chart: this shows the mean of the data and the error bars give an indication of the variability in the data.  Again you should have practised doing this in workshops and you have a step-by-step guide to remind you how to do this.  Remember you have a within-subjects comparison here.

You need to do three graphs:

  • One comparing mean right with mean left
  • One comparing mean vocal with mean silent
  • One comparing difference for right with difference for left (larger numbers mean that the difference between the silent condition and the speaking condition are larger, as you might expect if there was interference in the speaking condition)

Once you have got each graph you might want to edit it a bit. Remember that when you put the graphs in the report they need an appropriate title.

5. Finally, and most importantly, you need to carry out paired t-tests to test each of the hypotheses.

  • One comparing mean right with mean left
  • One comparing mean vocal with mean silent
  • One comparing difference for right with difference for left (the most important hypothesis)

Again you have a step by step guide to help you do the t-tests in SPSS.  Write up the findings in APA style. 

At this point you should have all the information you need for the results section of the report.

What to put in the results section:

  • An introductory sentence saying what was calculated for each participant.
  • The three graphs
  • Results of the three paired t-tests

It is helpful for the reader if you arrange it so the first graph is followed by the corresponding t-test results, then the second graph with the second t-test results, then the third graph and third t-test.


This is the section where you can speculate (within reason) and show your ability to interpret results and think about how they are relevant to the real world.

  • Summarise the three findings.
  • Are the results as predicted by the hypotheses or not?
  • How do findings differ from/ replicate those of previous literature?  Point out any similarities/differences in methodology.
  • What are the possible explanations for the results and which might be most likely, bearing in mind the nature of the tasks used in our experiment?
  • What implications might there be for using dual task methods to investigate brain organisation?   
  • Methodological flaws – can you think of any other explanations of the results?  Does your knowledge of the brain suggest any limitations of this method (think about whether functions are confined to one hemisphere, and to what extent there are individual or group differences)?  Might the results vary depending how participants are instructed?  Can you find any criticisms in the literature of previous experiments which might apply to our experiment too?  How could any issues be fixed?
  • Can you think of any further experiments which might be useful to answer any questions raised in the discussion?
  • Overall summary/conclusion

References and reading list for the practical

*Caroselli, J.S., Hiscock, M. & Roebuck, T. (1996). Asymmetric interference between concurrent tasks: an evaluation of competing explanatory models. Neuropsychologia, 35, 457-469. – available on Science Direct

*Kinsbourne, M. & Cook, J. (1971). Generalized and lateralized effects of concurrent verbalization on a unimanual skill. Quarterly Journal of Experimental Psychology, 23, 341-345. (On PSYM61 Canvas as a pdf)

*Klingberg, T. & Roland, P.E. (1997). Interference between two concurrent tasks is associated with activation of overlapping fields in the cortex. Cognitive Brain Research, 6, 1-8.

McGowan, J.F. & Duka, T. (2000). Hemispheric lateralisation in a manual-verbal task combination: the role of modality and gender.  Neuropsychologia, 38, 1018-1027. – available on Science Direct

Medland, S. E., Geffen, G., & McFarland, K. (2002). Lateralization of speech production using verbal/manual dual tasks: Meta-analysis of sex differences and practice effects. Neuropsychologia, 40(8), 1233–1239.

Wu, T., Liu, J., Hallett, M., Zheng, Z., & Chan, P. (2013). Cerebellum and integration of neural networks in dual-task processing. Neuroimage, 65, 466–475.

NB. * = Key Reference.

These references are available on line from the library journal databases.

You may not need them all and you will find that each of them only partly overlaps with what we are doing – it is your job to pull together information from a number of sources and convert it into a logical argument.

You will probably also need to consult a biological psychology textbook for information about brain organisation – most of it was discovered long before journals were around.  This is not necessarily a sufficient list – it is a bare minimum.  find more sources as w

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