Perception And Attention

1. Change detection has been a useful tool to study visual attention and short-term memory in visual perception. It demonstrates how an absence of focused attention can affect perception. The Hypothesis that researchers had was that the higher percentage of correct responses and the faster reaction time would correspond to no flicker condition on the other side, when flicker condition, the percentage correct would decrease and the reaction time would be slower. This difficulty to detect changes in scenes is called change blindness

Ronald Rensink and co-workers (1997) did a change detection experiment, in which they showed one picture, followed by a mask (blank field), followed by the same picture with an object missing (when changes) and the same image (when no changes). This procedure is performed at a very high rate and observers are told to click a button as soon as they see the difference between the two images. This method of studying change blindness has helped researchers discover two very important findings. The first finding is that it usually takes awhile for individuals to notice a change even though they are being instructed to search for a change. In some cases, it can even take individuals over one minute of constant flickers to determine the location of the change. The second important finding is that changes towards the middle of a picture are noticed at a faster rate than changes on the side of a picture. This is still commonly used in current research on change blindness and has contributed to current knowledge on change blindness.

2. The method followed in this demonstration lies in pressing “c” when u see some change between both images that are shown, or “n” if you couldn't see any change. So In half of the trials there was some change. On the other half of the trials the picture were different in some way.

For each kind of pair, either the pictures appeared immediately one after the other (no flicker condition), or a blank gray box appeared in between the pictures (flicker condition). Your task was to report whether the pictures were identical or differed.

The independent variable in this experiment was the flicker and no flicker conditions. Two dependent variables were measured: proportion correct judgments and reaction time. Proportion correct was identifying that the images were the same or different. Reaction time was the time between the appearance of the stimuli and the time when the observer made a response.

3. My results show that I have had two mistakes, both of them have been because I perceived that there weren’t changes, despite of the images changed in some way.

In these two trials, the were a common feature, the flicker condition, so that, it was a easier way to underestimate the changes, so I did mistakes in my change detection task.

My Data summary

Condition Proportion Correct RT (ms)

Flicker 0.75 7307.3335

No Flicker 1.0 5994.0

This is my data summary table, we can observe that when there is Flicker condition, the proportion of correct answers is 0.75 (75%), and when images are alternate without any blank field, my proportion correct is 1.0 (100%). Moreover the time used is perfectly refflected here. Reaction time(RT) is 7307.3335ms (mean)when flicker-condition, and 5994.0ms (mean) when not-flicker-condition. That means that when there is some blanck field between images, the time to respond is larger and the probability to make an error increases.

4.1. We come to the conclusions that under flicker

conditions observers can take a surprisingly long time to perceive

large changes in images of real-world scenes. This difficulty is not because of a disruption of the information received nor to a disruption of its storage. It does, however, depend greatly on the significance of the part of the scene being changed,

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