Cognitive processes effecting Heart Rate: Testing Lacey's Intake-Reject Hypothesis

Student Number: 151381

Cognitive processes effecting Heart Rate: Testing Lacey’s Intake-Reject Hypothesis

Abstract:

Lacey’s (1967) Intake-Reject Hypothesis was tested using data from 88 male and female participants. Two variables, task difficulty and type of task were manipulated to measure participants’ heart rate (in beats per minute). A 2x2 factorial Repeated Measures was performed on the data and the results were found to be in concordance with the theory Lacey had proposed. The implications of these findings are discussed with reference to Lacey (1967), and issues regarding validity and reliability are addressed.

Introduction

It is well known that heart rate changes when we experience different emotions. For example, your heart starts beating faster when a ‘scary’ scene occurs in a horror film, or you feel as if it skips a beat when you think you’ve seen a ghost. Detecting these changes is difficult and by making even more precise recordings of heart rate activity, other, smaller changes in heart rate (not necessarily related to emotion or stress) which may be associated with subtle changes in perceptual and cognitive processing (Hahn, 1973).

Instinct tells us tells that heart rate increases when we encounter difficult situations, or does it? Lacey (1967) argued that in some cases, this was not necessarily true. He offered a theory (1967) that proposed that when solving problems in your head (for example mental arithmetic), heart rate would indeed increase (the more complex the problem the higher the heart rate). Lacey argues that the reason for this is because this type of task requires participants to concentrate on their mental operations and to reject irrelevant information coming from the surrounding environment. In contrast, the theory predicts the tasks that do require mental intake of environmental stimuli, for example when performing a visual search task (the more difficult the visual search the lower the heart rate) will decrease heart rate. The theory therefore suggests that there is no simple, direct relationship between heart rate at task difficulty as, depending on the type of task, in can go either way.

Electrodes placed on the skin can record the electrical potentials that are generated by the heart. In our experiment we will use two electrodes, one will be placed on the sternum and one on thee out side of the participants’ left ankle (the electrodes need to ‘cross’ your heart). When these recordings are amplified, a typical waveform becomes visible (see figure 1.), which is called the electro-cardio gram (ECG). From the ECG heart rate can be calculated by measuring the time taken between two R-waves (the most prominent wave) and by using the following formula:

Heart rate (HR) – 60 / time between two R-waves (in seconds)

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Heart rate (HR) – 60 / time between two R-waves (in seconds)

This study seeks to test Lacey’s intake-reject hypothesis. There will be two independent variables to the tested, the first of which being the type of task undertaken. There will be two types of task: Mental arithmetic (an example of rejecting environment, therefore increasing heart rate) and Visual Search (an example where intake from environmental factors is required, leading to a decrease in heart rate. Each type of task will have two levels of difficulty (Hard and Easy), thus resulting in 4 experimental conditions: Easy Visual Search, Hard Visual Search, Easy Mental Arithmetic, Hard Mental Arithmetic. It then follows that the experimental hypotheses of this study be:

1) The hard mental arithmetic tasks will increase heart rate and the hard visual search tasks will decease the heart.

2) The type of task performed will have an effect on heart rate as will the level of task difficulty.

Method

Design

A Repeated measures design will be used it this study. There are two independent variables each with two levels being manipulated, those being: type of task: (Mental Arithmetic, Visual Search); and task difficulty (Hard, Easy). The dependent variable was the participant’s heart rate in each of the 4 conditions, measured by the ECG. Our heart has a number of vital functions to be performed on a continuous basis and therefore is always active. The important function of pumping blood round the body has first priority and any psychological changes are minimal and need several trials and large participant populations to show effects. The variance attributable to psychological factors is relatively modest. Also, given that individuals vary in the patterning of their heart rate (unless vary large populations are used) tend to be repeated measures designs (i.e., within participant studies).

Participants

110 psychology students from the university of Portsmouth participated in this study however only the data from 88 of those participants was used as the rest were deemed unreliable. The gender ratio was unrecorded however was estimated to be 5 Females: 1 Male. The age range was 19-45, the mean age was not recorded

Materials

An Electrocardiograph was used to measure the participants’ heart rate. Participants were attached to two electrodes (one on the sternum and the other on the left ankle), which were connected to the Cardio-tachometer that recorded the heart rate. Participants were asked to complete an Informed Consent Form (See Appendix) before partaking in the study.

Procedure

Once wired up for Heart Rate (HR) recording the participant was asked to sit comfortably at a table in the testing chamber, with two experimenters. One experimenter (E1) presented the task materials and instructions, the other (E2) timed the task periods with a stopwatch. Each of the four task conditions lasted 90 seconds, after checking that the HR equipment was working, E1 stated ‘start’, started the stopwatch, and pressed an event recorder button to mark the pen record. E2 presented the first condition to the participant. After 90 seconds, E1 stated ‘stop’ and zeroed the stopwatch. This procedure was repeated until all four conditions were completed. All four conditions were randomised to counteract any order effects. The number of correct responses was also recorded for each participant. The following instructions were read out to each participant at the start of the study.

“You are going to have several things to do. My colleague will tell you when to start. Two tasks involve mental arithmetic. For these tasks, I will read out problems. You will work out he answer in your head and write it down. You must solve those problems in your head and write only the answers on the paper. Do not do any calculations on the paper. Please work quickly and efficiently. In the two other tasks you will have to check off individual letters among a set of other letters. Again please work quickly and efficiently. Never rush but work with full concentration. The whole procedure will be finished in about 7-8 minutes. Please sit in a relaxed fashion throughout the experiment. Too much body movement will spoil the heart rate record.”

Results

(See Appendix for full SPSS output )

A 2-way factorial ANOVA (for a repeated measure design) was performed on the data. From Table 1 below , it can be seen that a significant main effect for Task Type (F1,87 = 25.325, p < 0.001) was observed suggesting that reaction time varied as a function of visual field presentation. An interaction effect between Task Type and Task Difficulty was also observed suggesting that heart rate does indeed differ depending on not only the type of task performed, but also the degree of difficulty of that particular task (See Figure 1). However, it can be seen that a significant main effect for Task Difficulty was not observed (F1,87 = 11.605, p = 0.232) suggesting participants’ mean HR did not vary as a function of the task difficulty alone.

Table 1

Figure 1

A 2-tailed, paired-samples, related t-test was performed on the number of correct responses given by the participants and a significant difference ( t(1,87) = 30.315, p < 0.001), was found between the number of correct responses given between the level of difficulty of the tasks. See Table 2, below.

Discussion

As can be seen from the results there is clear evidence to show that there is no direct relationship between task difficulty and heart rate. The results show that there is a highly significant difference (F1,87 = 25.325, p < 0.001) in the mean heart rate between the types of task performed by the participant however they also show that heart rate is not significantly effected (F1,87 = 11.605, p = 0.232) by the level of difficulty of the task. There is, however, a significant interaction effect between the two variables suggesting that there is a relationship between the type of ask preformed and its level of difficulty and together, they affect heart rate. The results from the t-test show that there is a significant difference in the number of correct responses for each task, with the least number of correct responses being in the Hard Mental Arithmetic condition and the most amounts of correct responses occurring the Easy Visual Search condition. The experimental Hypotheses are therefore accepted; although there is no direct relation ship between heart rate and task difficulty, heart rate can, in fact, change depending on the type of task presented; tasks requiring the rejection of information from the environment (mental arithmetic tasks) were proved to produce a faster heart beat and tasks that required the intake of information from the environment (visual search tasks) were proved to produce a lower heart rate. This supports Lacey’s (1967) Intake-Reject hypothesis that High Mental Arithmetic (HMA) tasks will produce a higher heart rate than Easy Mental Arithmetic tasks (EMA) and High Visual Search (HVS) tasks will produce a lower heart rate in comparison to Easy Visual Search (EVS) tasks.

It is interesting to note that task difficulty has no significant effect on heart rate alone, as this would have been a logical conclusion to come to given that heart rate tends to increase with stress. However, this does support Lacey’s theory that difficult tasks requiring rejection of external information will produce a higher heart rate than easier tasks requiring the same rejection of information. A reason for this could be because these type of tasks much more mental input by ourselves that others and it is possible that participants can anticipate greater mental stress, resulting in an increase in heart rate. Task difficulty also comes into play when dealing with situations requiring the intake of environmental stimuli, with harder tasks producing a decrease in heart rate.

One of the main limitations of this study is that no control was made for the possibility of other factors affecting heart rate, such as stress, illness etc. Participants who may have been suffering from stress-related diseases may have a higher heart rate thus affecting the reliability of the results. The participants were students partaking in a class experiment and may have had previous knowledge that could influence their reactions to the tasks. For example, if the participant knew we were testing Lacey’s theory and had prior knowledge of the intake-reject hypothesis, they could manipulate their responses, which would affect the validity of the results. Also, the participants, all studying the same course, at the same university, may well have told other participants who had no yet taken the test what to expect. Preparing for the tasks, emotionally as well as mentally, may well have an effect on their performance in the study.

The study conducted gave sufficient results for the research questions, but there are other areas that could be investigated if the study were to be replicated. We would compare different levels of difficulty (more than two) and also different types of tasks that require Intake-Rejection of environmental stimuli comparing them to one another. Also it would be interesting to see if age and gender play a factor in rise and fall of heart rate with specific reference to these types of tasks. It would be interesting to see if there was a biological difference in the heart rate responses of males and females to type of task given and their performance at various difficulty levels. Furthermore, different populations could be examined, testing for any possible cultural differences that may have an effect on heart rate during problem solving. As mentioned above, it may also be an idea to test to see if preparation for the tasks has any effect on heart rate during performance, if the participants know what to expect from the tasks, their physiological responses may differ from when they do not know what to expect.

In conclusion this study has indicated that although there is no direct relationship between task difficulty and heart rate, levels of difficulty with the types of task performed do have an effect on heart rate, as do the types of tasks. This supports Lacey’s Intake-Reject Hypothesis suggesting that heart rate can, in fact, change depending on the type of task presented; tasks requiring the rejection of information from the environment (mental arithmetic tasks) were proved to produce a faster heart beat and tasks that required the intake of information from the environment (visual search tasks) were proved to produce a lower heart rate.

References:

Hahn, W.W. (1973). Attention and heart rate: A critical appraisal of the hypothesis of Lacey and Lacey. Psychological Bulletin, 79: 59-70.

Lacey, J.I., (1967). Somatic response patterning and stress: Some revisions of activation theory. In: M.H. Appley and R. Trumbull (Eds). Psychological Stress: Issues in Research. New York: Appleton Century Crofts, pp 14-37.

Pinnel, J.P. (2003). Biopsychology 5th Ed. Pearson Education Inc.