Method

The group of participants contained both males and females; all were Psychology undergraduate students aged 18-21. Participants used a computer program which displayed the instructions and experiment on-screen.

In the first condition, participants were shown only a test stimulus. This was either the capital letter “R” or the number “2” in one of six different orientations (0°, 60°, 120°, 180°, 240°, 300°), and was either the right way round or mirrored. In the on-screen instructions, participants were asked to respond as quickly as possible, pressing one key if the character was the right way round, and another key if it was mirrored. This was repeated 96 times.

In the second set of tests, the stimulus was preceded by two cues. First, an identity cue was given for one second, showing whether the coming test stimulus would be “R” or “S”. Then, an arrow was shown as an orientation cue, for either 400 or 1500 milliseconds. The participants were asked to make the same judgments as in the first condition. Again, this was repeated 96 times, with a mixture of 400 and 1500 millisecond cues (400ms should be too fast to use as a cue, while 1500ms should remove the effects of orientation).

Results

The individual results were collated and mean response times were calculated for each of the three conditions. The graph of clockwise angles shows whether or not the response times were symmetrical around 180°, and the graph of shortest angles forms a linear relationship upon which we can perform linear regression.

The graph of clockwise angles below shows that the results are approximately symmetrical around 180°, although the reaction times in the 400ms cued condition are slightly faster at 240° and 300° than at 120° and 60°, their equivalent shortest angle. The opposite is true for the no information and for the 1500ms cued conditions. However, the differences are small.

Linear regression

Linear regression is used to measure the correlation between angle of rotation and reaction time. The null hypothesis is that there is no correlation between angle of rotation and reaction time. Using the shortest angle graph, the linear regression equation, the r-value (correlation coefficient – a measure of the how well the regression line fits the data) and the t-value (significance of r) were calculated for each condition.

The methods used to calculate the r-value, the t-value and the linear regression equation are shown here for the no information condition:

871

The critical value of t (for two-tailed, p=0.05, 4 degrees of freedom) = 2.776, so there is a significant correlation between angle of rotation and response time in the no information condition.

Below are the results for the rest of the conditions.

This shows that for all three conditions, there is a significant correlation between shortest angle of rotation and response time. The probability of these results being observed if the null hypothesis were true is less than 0.05.

One-sample t-test

As a significant correlation was found, a one sample t-test was performed, to see if there is a significant difference between reaction times in the cued and un-cued conditions. The null hypothesis is that the difference between the response times in the cued and un-cued conditions is zero.

The calculations for the t-test on differences between 400ms cue and no information are as follows:

The t-value for the differences between the 1500ms cued and no information conditions is 7.51. The critical for a 2-tailed t-test, p=0.05 is 2.571. Therefore for both cue times, there is a significant difference compared to the un-cued condition. The probability of seeing these results if the null hypothesis were true is less than 0.05.

Discussion

The idea of having cues for 400 and 1500 milliseconds was that 400ms would not be long enough to prepare, meaning that the cue would be less salient than a cue that was displayed for 1500ms. However, at angles other than 180°, there is little difference between reaction times after a 400ms cue and a 1500ms cue. In fact, at 240° and 300°, responses were on average slightly faster after the 400ms cue than the 1500ms cue. This indicates that maybe 400ms was too long a time for a “short” cue to be displayed, as there was enough time to prepare. However, there is an obvious difference between response times to 400ms and 1500ms cues when the test stimulus was presented at 180°.

For the no information and 400ms cued conditions, the points appear to closely fit a linear equation for 0°, 60° and 120°, but the reaction time for 180° seems to be higher than the other points would predict. One possible reason for this effect is that you have to make a decision about which way to rotate the image. At angles other than 180°, the direction of the shortest angle of rotation is obvious; perhaps the extra response time at 180° is due to this decision delaying the rotation. When the cue is shown for 1500ms, you have more time to prepare to see something at an orientation of 180°, so this minimises the effect of making the decision.

We expected to find that the 400ms cue would show no difference to the no information condition responses. However, we found that it gave more similar responses to the 1500ms cued condition. The no information tests came first, while the 400ms and 1500ms cued tests came second, so part of the difference between the cued and un-cued conditions may simply be due to practice. A way to investigate this would be to have another test group who encounter the cued conditions first, then the un-cued. If the response times for the cued condition increased, and/or those for the un-cued condition decreased, then we could conclude that practice does have an effect. Alternatively, if the results were the same, then the differences are caused by something else.

The 1500ms cue was supposed to give plenty of time for participants to mentally rotate the identity cue to the angle shown by the orientation cue, eliminating the effects of orientation. However, there was still a strong positive correlation between shortest angle of rotation and response time, showing that the effects of orientation were still present. It may be that participants still mentally rotate the target stimulus to the upright position, and that the improved reaction times are due to either cued attention to the correct starting orientation, or simply due to practice effects as mentioned above. On the other hand, the longer cue exposure time of 1500ms does have a regression line gradient of 2.032, compared to 2.871 and 2.686 for no information and 400ms respectively, so perhaps some of the effects of orientation are eliminated.

Statistical analysis has shown that for both of our null hypotheses, the probability of seeing these results if the null hypothesis were true is less than 0.05. There is a significant correlation between rotation angle and response time for all three conditions, and there is a significant difference between response times in cued and un-cued conditions. However, we cannot draw any conclusions about the effect of the duration of exposure of the cue, as the results are ambiguous.