Although the mind has the capacity to process multiple tasks at the same time, it's efficiency processing these is subjected to the complexity of the task. Two main theories on this are brought forward ; A filter theory and a Cognitive Capacity Theory. The experiment was constructed in a way such that it was possible to examine Reaction Times of secondary task and correlate these results with a perception task and a semantic task. The results showed that the reaction time was faster when there was a less complex primary task set, giving validity to both theories.
Introduction
Divided attention occurs when at least two different inputs are received and these are all attended to (Eyseck 1990). Early work on this field explained attention in general with the Filter theory, whereby at some point after information enters the brain it is filtered so that it could be processed separately. Broadbent (1958, cited Best) suggests an early filtering of this information, while Treisman (1964, cited Best) postulates a process of attenuation before the information is filtered. Deutsch and Deutsch (1963) also have a theory, where all stimuli are processed, but only selected information filters into our memory capacity. The theory was termed Late Selection, compared to Broadbent's Early Selection.
These researchers centered on focused attention, and their work does not convincingly mould itself to divided attention. These theories explain divided attention as being a rapid alterations of attention (Allport et al, 1972), rather than a concurrent processing of stimuli.
Johnston and Heinz (1978) build on these late and early selection theories by combining them. And they also added a very important idea to their theory : efficiency to deal with information and the ability to move consciously between attention modes. Their theory has been called the "spotlight" effect (Best, 1992), because it can, like a spotlight be focused on a certain spot, or be made for a general, but less efficient field. As the system moves from early to late modes of attention it loses selection efficacy, but gains breadth of attention (Johnston and Heinz, 1978).
Kahneman (1973, sited Best) proposes a theory that is more compatible with divided attention. He stipulates that the mind has a limited amount of resources to process information. The number of resources used depends on the complexity of the task. Hence a complex task would use a lot of resources, thereby leaving little resources for other tasks. In this model, we can account the fact that we can perform many simple tasks simultaneously, but have problems performing multiple complex tasks at the same time.
This experiment will look at the effects that difficulty of primary task will have on the reaction time of a secondary task. Given the cognitive capacity model for attention, it is hypothesized that performance on one task will decline if a second task is attempted simultaneously when the sum total of the processing demands exceeds capacity (Best).
Method Subjects
414 participants where selected from the pool of first year psychology students at University of Sydney. This sample varied in gender, ethnic and socio-economic backgrounds. Participants where encouraged to do the experiment as part of their studies, and performed the experiment during their weekly allocated tutorial times.
Apparatus
A Macintosh Performs 5400/160 computer was used for the experiment, using a program called "Divided Attendant". The computer had an easily readable screen and a computer mouse with buttons wide enough to be hit easily by the participants.
Materials
Participants where given a list of 240 words on a two sided A4 page. Each side of the page consisted of 120 words, arranged into 4 columns of 30 words. One side was a list of randomly chosen words that could easily be classified by participants to be in three distinct categories ; Cookery words, Animals and words associated with Seascape. Each column of 30 had 10 words of each of these categories, arranged in a random order. The other side of the paper had the three categories randomly arranged into the four columns, again, making sure that there were 10 words from each category in each column.
The stimuli involved in the experiment where the same words which appeared on the sheet of paper, which where presented on the computer screen following the order of the sheet. The words where presented at a rate of 1.5 seconds. The other stimuli presented was a black square of approximately 7cm in length. The square appeared in the middle of the computer screen, and was easily recognized as the main stimuli.
Design
The 240 participants where randomly allocated into pairs, and these pairs where told to go to a computer terminal. Once this was done, the each person in the pairs where allocated as either participant "A" or participant "B". Two participants where used so that while "A" was taking part of the experiment, "B" could ensure that his partner was performing the task correctly, and vice versa.
The independent variable in the study was the reaction time taken to press the mouse button after the square stimulus was presented on the screen. The computer program recorded this reaction time. The control variable consisted of the words that where flashed onto the screen.
It was also necessary to include a preliminary test to record the individual simple reaction times of each participant. This would then form the individual's baseline RT, to be used as a controlled variable. The independent variables where in all cases measured and tabulated to this control figure. This was done to try and standardize the results, and to make them comparable to each other, accounting for individual differences.
All instructions for the experimented where given on the computer screen.
Procedure
Participant B was first given the sheet before mentioned and was told to read it in such a way that participant A could not read it. Participant A was then directed to practice the first part of the experiment termed "Read Words". The words where flashed on the screen at regular 1.5 second intervals. The participant was told to read the words out loud, and when the square stimulus appeared, they where told to press the mouse button as fast as they could. Participant "B" read the page and verified that the words where said. After a practice run of 30 words (the first column of the sheet), the participant did the experiment, while the computer recorded the RT of mouse pressing.
In the second part of the experiment, participant B handed the sheet to participant A. Participant A read the other side of the paper (the side containing the name of the word Categories) in such a way that participant B could not see them. Participant B then practiced the second part of the experiment termed "Name Categories". This part consisted much the same as the first part, except that the participant had to say out loud the category which the word belonged to instead of just reading it. Again, after the practice round of 30, the participant began the experiment, with his RTs recorded and participant A verifying that the his partner was indeed saying the right categories.
Results
The reaction times where collected and tabulated using a One Factor ANOVA. The P value in the results was 0.0001, showing that there is little chance of the results being caused by an error. Taking the mean RT for the three task, the fastest reaction time was the Simple RT (0.347sec), followed by "Read Words" RT (0.49) and slowest being the "Name Category" RT which was 0.783. Furthermore, a Scheffe F-test of the comparisons shows a significant difference between the simple RT and "Read Words" RT (23.306), the simple RT and the "Name Categories" RT (218.053) and "Read Words" and "Name Categories" (98.785).
Analysis of this data suggest that there is a significant change in RT across the three conditions. It also suggest that the change is increasing across the conditions.
Discussion
The results suggest that the complexity of the primary task has a direct effect on the secondary task. These findings fit in well with the interpretation proposed by Kahneman. Under his model, the semantic task would require more resources, leaving less resources for the reaction task. The reading task did not require as many resources, hence leaving more for the reaction task.
The findings are also support Jhonston and Heinz (1978) proposal of a multi modal system. The easier tasks where processed earlier, therefore leaving more cognitive capacity for the secondary task, while the semantics task would be processed later and would leave less capacity for the secondary task.
There are several shortcomings in the experiment. Although two participants were placed in pairs to ensure that his partner followed the primary task, there where no recorded results. If there was an error in the primary task, the participant was told to keep going. It would be advantageous for the study to correlate the reaction time with the errors made in the primary task. It is difficult to speculate on the results of such a project. When an error occurs, we would have to establish whether it the stimuli was hard to comprehend, or whether an answer was given without thinking. In the first scenario, the theories would predict that the reaction time would be slower, since there would be more cognitive capacity devoted to it. But in the latter case, one would expect a faster reaction time, since there are fewer resources used. The findings from such an experiment would help explain our capability to process different information at the same time.
The choice of words could also be reconsidered. Certain words are ambiguous and could be classified in two or maybe three of the categories. "Clam" is at the same time an animal, a term for cookery and part of the seascape. Another problem in choosing words was the assumption that all participants where able to easily distinguish the words.
Further studies into the two theories could be made in light of experiments done where practice of a task is thrown into the equation (Spelke et al, 1980). They discovered that they could train people to do two complex tasks simultaneously. Capacity theorist might argue that this is due to a certain behavior becoming automatic, but it doesn't account for the comprehension of both the tasks.
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