Abstract
The study uses the Posner paradigm to determine whether the condition of the cue can affect the reaction time of the subject. Most importantly is that the eye movement was prohibited. Using the data of 143 subjects, the ANOVA method and Bonferroni corrections, we have found out that the condition does influence the reaction time, however the difference between the cues is not significant Nonetheless the reaction time was far off from the target 100 ms due to inexperience and not understanding of the task set before the subjects. The results of the study have shown us two processes that are going on in the course of the tests: acceleration and braking the duration of which affects the results and thus the whole study.
Introduction
It is possible to use the term "focusing" meaning as setting attention to a particular source, which may be a sensory input or the internal structure of a semantic memory. The term "focusing" is closely linked with the concept of "reflex", which manifests itself in a variety of changes of CNS activity and behavior. However, the concept of the focusing reflex does not separate attention and the arising from it perception of the stimulus.
Another cognitive act different from focusing is called detection. Under detection we mean the case when the stimulus has provided a level of activation of the nervous system, in which a subject can give an account of its presence by an arbitrary response, which is defined by the experimenter. The answer may be verbal ("I see") or manual (pushing the button). Detection refers to the awareness or perception of the stimulus. Detection and Differentiation of focus allow us to empirically test the hypothesis that certain reactions (for example, the saccadic eye movements) can be caused by the stimulus before it was even detected. Hence it follows logically that the normal subject can move his eyes in the direction of the stimulus, while not being able to somehow else report about it (Tipper, Iordan and Weaver, 1999).
It is also important to distinguish between external and central control over focusing. If the focus on the content on the memory system and the external stimuli events have a common basis, it becomes clear that we can focus our attention to the absence of an external stimulus. Similarly, the eye movement can be controlled by an input stimulus or result from internal search plan.
Obvious is that spatial attention shifts include something besides the eye movements to specific locations in the visual field. Of course, no one will argue that there is a close connection between the eye movements and shifts of attention. However, there is always the assumption that the attention can be moved irrespective of eye movement. For example, Tipper, Iordan and Weave (1999) have pointed to the ability to separate the line of sight with the direction of attention.
Many experimental studies using mental chronometry methods have failed in attempts to prove this ability, at least in the empty visual field. More recent studies have reported shifts of attention without eye movement have become more frequent (Posner, Nissen, Ogden, 1978, etc.).
Method
We have tried to determine whether the response time for focusing on an object is faster when subjects know where the stimulus will be presented, compared to situations where they do not know about it. The study focuses on the time difference in reaction to stimuli appearing at the expected and unexpected positions in the visual field, as a measure of the efficiency of detection by the expected direction of focus position. To ensure that changes of the response time does not depend on the eye movements, the eye-movements were tracked using the electro-oculography method. We have analyzed all samples of the 143 participants with over 80 trials completed by each.
The trials were performed in the school lab using Dell computers and special software. Each subject was to log in and check whether the whole area was easily observed prior to starting the lab. The subject is shown a fixation point (in the form of a red square) which appears for a short time and then fades. At random times a cue is shown in the form of a directional arrow. If it points right then the condition is that the target will appear on the right with an 80% chance. However, if the arrow points to the left, there is an 80% chance that the target will also be on the left. If no fixate point appears then the target will appear center with an 80% chance.
Each subject was set the task of shifting his attention on to the fixation point (red square) as soon as it appears no matter where its location will be. And as soon as the fixation point has been noticed the subject is to press the left mouse button to confirm the trial. Most importantly is to keep focused on the center position where the fixation point was shown first and not move the eyes at any costs. As soon as the 80 trials are over the subject is to save his results and pass onto the next window which will include a debriefing, his results, the data of the group and global data.
We are focusing our study on the independent and dependent variables received from the studies. The independent variable is the cue shown to the subject. It could be either invalid (arrow points in the opposite direction to where the red square actually did appear), neutral (no cue or not even an arrow) or valid (the arrow did actually point to where the red square appeared). The dependent variable on the other hand was the response time, or reaction between the time the red square appeared and was noticed by the subject.
Results and Figures
We have used the analysis of variance (ANOVA) method to analyze the available data using the independent variable of condition (invalid, neutral and valid) and the dependent variable as the reaction time of each trial between the appearance of the red square and the subjects reaction to its appearance. As a result we have noticed that the time of reaction was not that much different. The reaction time under the neutral condition was the largest due to the subjects being unsure in the choice they were to make (Fig. 1).
We have also used the Bonferroni corrections to show the differences between the invalid condition (MS = 345.28) and the neutral condition (MS = 373.28), which was not significant (SD = 27.90). The difference between the neutral condition and the valid (MS = 326.78) was more significant (SD = 46.49), however not large enough to cause concern. And the difference between the valid and invalid conditions was even less (SD = 18.59).
Discussion
It was assumed that the response time would have been the fastest for valid conditions and slowest for invalid. However, the results of the study have shown that the slowest reaction time was under the neutral condition. It is clear that the valid cues signaled the subjects about the location of the red square and if it was not in position the instantly pressed the button acknowledging its presence in the opposite direction. This pattern shows that the information was processed very quickly as the reaction time is quite small. The majority of troubles were with the neutral condition when the subjects were at a loss with no clear conditions and cues as to where the red square was to appear. Therefore seeing this pattern, it is logical that the reaction time for the neutral condition is by far larger than the valid and invalid conditions. Besides acknowledging the valid cue allowed the subjects to transfer their attentional focus without moving their eyes to the location of the target thus increasing the reaction time of their response. The invalid condition on the other hand made the subjects shift their attentional focus to the wrong side, thus increasing the time of their response.
Though it was planned that the effect would not be very large (not exceeding 100 ms) in reality they were quite long. The difference between the time of reaction is significant due to the implemented condition. All subjects had difficulties with acknowledging the presence of the red square and reacting.
It is important to ask ourselves of the sufficiency of the degree of change in the efficiency, that we see when moving the subjects focus, so that we can measure the time of reaction. Jonides (1981) received one of the proofs of such timing. In studies similar to the one we have just described, he varied the time interval between the cue and stimulus. Jonides was able to clearly identify the temporal dynamics of efficiency changes up to a few hundred milliseconds. He also found a very clear distinction between the temporal dynamics of efficiency in cases where the subject is brought to the attention of a certain spatial position by means of a peripheral cue (valid and invalid), and when the neutral cue was up. The difference between neutral and peripheral cues is especially important when the future studies will turn to the analysis of the relationship between time-bound movements of attention and eye movement.
We got two effects that occur when peripheral cues are presented. We assume that these two effects are overlapping in time and that the detection efficiency is a result of their combined effect. The first effect is acceleration, which we believe is central, since it can be generated as a symbolic hint, indicating the place in space where, perhaps, there may be an incentive to the target and peripheral cue. We believe that the acceleration is caused by the hidden clues in the focus of attention towards the target. The focus can be caused by both neutral and peripheral cues (Posner, Nissen and Ogden, 1978), to appear before the eye movement (Posner, Nissen and Ogden, 1978) or as a result of manipulation of probability (Posner and Cohen, 1984).
Second, is the braking effect with a decrease in the efficiency of detection of the target stimulus. We can find a clear dividing line between, and prompted by the non-cued positions only when the attention is prompted by the position contrary to the neutral point of fixation. However, we suggest that braking occurs at about the same time as the acceleration, but is only masked by more powerful acceleration, which is a latent orientation. The braking effect is off-center origin, since it only occurs when the peripheral cue is up. Braking occurs regardless of whether prompted by eye focus shifts to the target or not (Posner, 1986).
Our point of view is that acceleration effect relates to the focus of visual attention in a fixed field, while the braking effect is associated with the preference of the new position as targets for future eye movements. We can also consider the effect of the brake release as a result of the attention of the spatial position, whereby the focus on any of the positions does not become excessive. However, the fact that the braking depends on the peripheral visual changes and can last for such a long time after the eye movement, casts doubt on its significant role in the management of future acts of covert and overt focus (Rorden and Driver, 2001).
This phenomenon has to be studied more as the current study experienced certain limitations. It appears that the subjects did not quite understand the task as the first trials took much longer than the ones in the end. Besides, the study was limited in the number of workstations where the subjects could pass their trials.
References
Jonides J. (1981). Voluntary versus automatic control over the mind’s eye’s movement. In Attention and Performance IX edited by Long J.B., Baddeley A.D. Hillsdale, N.J.: Erlbaum. p. 187-203.
Posner M. (1986). Chronometric explorations of mind. N.Y., Oxford: Oxford University Press. 271 p.
Posner M. and Y. Cohen. (1984). Components of visual orienting. In Attention and Performance X edited by Bouma H. and Bouwhuis D.G. Hillsdale, N.J.: Erlbaum. p. 531-556.
Posner M, Nissen M. and W. Ogden. (1978). Attended and unattended processing modes: The role of set for spatial location. In Modes of perceiving and processing information edited by Pick H.L. and Saltzman I.J. Hillsdale, N.J.: Erlbaum. p. 160-174.
Rorden C. and J. Driver. (2001). Spatial deployment of attention within and across hemifields in an auditory task. Experimental Brain Research. Vol. 137. p. 487-496.
Tipper S.P., Iordan H. and B. Weaver. (1999). Scene-based and object-centered inhibition of return: Evidence for dual orienting mechanisms. Perception and Psychophysics. Vol. 61 (1). p.50-60.Annex 1
