Change Blindness: Impact of Congruency
Change Blindness: The Impact of Congruency on Visual Perception
This experiment used a within-participants design to test if change blindness is altered depending on the type of change made. The independent variable had three conditions: congruent change, incongruent change, and within-category change. The dependent variable was measured by the time (in seconds) students took to detect changes in each condition. A control measure, where one-quarter of the images did not include any change, was used to prevent unreliable data and avoid participants expecting changes in all images.
Participants
Two hundred and fifty students (79 males, 171 females) from the DE 200, 2016 module participated in the study as part of the module activities. The participants’ mean age was 35.31. Participants signed an informed consent form before taking part in the experiment. As students of the DE200 module, they had some general knowledge about experiments, although they weren’t yet experts in the area.
Materials
The stimuli were created using a computer. Sixteen everyday scenes (common places people see in their daily life, like a kitchen or bathroom) were used, with one pair of images per scene. Each image was presented for 240 milliseconds (ms), followed by a brief intervening blank for 80 ms. After the blank, the image appeared again with a change. This method is called the “flicker method” (Rensink et al., 1997; Briggs & Davies, 2015). Each scene lasted for 0.25 seconds, and students had to click on the image if they detected a change. The time was automatically recorded once the student clicked. One-quarter of the images had no change to prevent students from clicking on all images.
The images had three types of changes:
- Within-category changes: One object changed for another of the same category (e.g., a computer was changed for a laptop).
- Congruent changes: The object changed didn’t belong to the same category but was related to the scene (e.g., a cup of tea was replaced with a cup of water).
- Incongruent changes: The object replaced wasn’t related to the scene and didn’t belong to the same category (e.g., a book in a room was replaced by a plate of food).
In the first image, there was the original picture, then the blank screen, and lastly the modified image. If the change was made to a cushion, the type of change was a within-category change. The numbers at the bottom indicate the seconds remaining before the next scene started.
Procedure
Each student participated individually. They needed a computer and an internet connection to access the online experiment. Before the experiment, participants had a practice trial of three scenes, which were examples of the scenes they would see in the experiment. After the trial, they started the real experiment, which consisted of 16 everyday scenes. The order of the scenes was randomized, and each scene had almost two identical images, which appeared alternately with an intervening blank of a quarter of a second between each scene. The scene lasted for 20 seconds, and students had to detect possible changes before the time elapsed. If they detected a change, they had to click on the image, and the time taken was recorded automatically. The images flickered, so it was advised not to do the experiment if any student had photosensitive epilepsy. Participants were provided with a debriefing sheet explaining that the experiment was investigating change blindness and that the purpose of the study was to see whether the type of change made to the image would affect the likelihood of detecting the change. The overall length of the experiment was a maximum of 4 minutes.