The results of this study must be seen in light of some limitations. This thesis is based on an experiment using a routine task. The task demands a steady level of attention from the
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participants to provoke an effect from the different conditions. Time spent on a task is described as giving both negative and positive effects, depending on the type of task (54). Being a routine task with 400 trials, the experimental manipulations are possibly affected by time a negative manner, making it more demanding to allocate cognitive resources and possibly reducing the LC – NA activation. This is not controlled for in the data analysis, but was targeted when setting up the experiment with short breaks at every 50th trial.
A limitation in the analysis of the response times and pupil data is the inclusion criteria, since only correct response trials are included. This might be reasonable, as erroneous responses are known to activate frontal networks associated with attentional control (55), possibly also interacting with the LC – NA system (56). However, the analysis is of two separate sets of trials, the incorrect trials with the error – rates and the correct trials with response times and pupil dilation. A possible problem is that the dependent variables are not analyzed from the same set of trials, implicating theoretical limitations when we are comparing the data and expecting them to correlate as a result of cognitive control mode. Furthermore, there may be a loss of effect size in the analysis the response time data and pupil data when the incorrect trials are not included.
The strengths of the study are the systematic nature of the experiment, enabling control of unwanted factors. The AX – CPT is a popular experimental design, so previous studies using the method make up a solid empirical basis for comparing results. This provides a foundation for interpreting the results, and understanding unexpected effects from the experiment.
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6 Conclusion
In spite of possible limitations, the results of this study add knowledge about the specific effect of the cue – manipulations and the pupil dilation after response. The experimental paradigm had an opposite effect on response time and pupil dilation in the dual AY – trial and an unexpected effect at the same measures in the dual BY-trial, thought to be a result of spatial cueing. There are areas of improvement regarding future studies using pupillometry. One of them is gathering a solid empirical basis about the pattern of the pupil response, and which time segments to focus on, e.g. maintenance interval versus response phase. The present study shows correspondence between behavioral data and pupil data in the response phase. Further knowledge would help developing more sensitive and specific analysis of the pupil response, and give insight about the role of LC – NA activation in cognitive functioning.
Acknowledgement
This study has been carried out at the Faculty of Medicine and in cooperation with the Faculty of Social Science, Department of Psychology of the University of Oslo. I am particularly grateful to my supervisor Thomas Espeseth. His comments and suggestions related to the experiments, statistics and presentation have been greatly appreciated. Special thanks to Thomas Hagen at the Department of Psychology, who was of vital importance at the cognitive laboratory in helping me planning and executing the experiment and preprocessing the data.
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Appendix
Figure 10: Stroop inhibition task. Participants were told to read the color of the letters instead of the name of the color written
Figure 11: Letter – number span. Letters and number s were read - out in random order; the participants were told to read them back in alphabetical and chronological order.
Figure 12: Ravens Progressive Matrices. Each task consists of nine matrices in a logical pattern, but one part is missing. The participants are told to choose on out of the eights alternatives that fits the pattern. The difficulty progresses with each matrix.
0 1 2 3 4 5 6 7 30 - 35 36 - 40 41 - 45 46 - 50 50 - 55 56 - 60 60 -65 N o . o f p ar ticp an ts
Words completed in 30 seconds
Stroop inhibition task
0 1 2 3 4 5 6 7 8 9 9 - 10 11 - 12 13- 14 15 - 16 17 - 18 19 - 20 N o . o f p ar tici p an ts
No. of letter - numbers sorted and repeated (max 20)
39 0 1 2 3 4 5 6 7 8 19 - 20 21 - 22 23-24 25-26 27-28 29-30 31-32 33-34 N o . o f p ar tici p an ts
No. of correct matrices in 40 minutes (max 36)