The McGurk Effect

For my class presentation I demonstrated the McGurk effect. If you watched the video in class, you should have heard the speaker say “tha-tha” or “da-da” as you watched the speaker, and “ba-ba” as closed your eyes. This is due to the McGurk effect, an illusion that demonstrates our perception of speech is influenced not only by the auditory sensation of speech, but also visual information about the speaker’s mouth forming the words. This is an example of multi-modal perception: perception formed by inputs from more than one sense modality, such as hearing and sight. The McGurk illusion is created by dubbing “ba-ba” over video of a speaker saying “ga-ga.” The auditory input of “ba-ba” and the visual input of “ga-ga” fuse into a perception of “da-da” as the brain tries to make sense of the conflicting information.

The McGurk effect is interesting among examples of multi-modal perception because the conflicting information from hearing and sight leads the brain to fuse the sense information into one perception, rather than one sense completely dominating another. For another example of auditory information affecting visual perception, take a look at the motion bounce illusion. This illusion is much less drastic than the McGurk effect, but it shows how audition can influence how we perceive events in visual space.

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Negative Afterimage

Reber Shukri Professor Vaughn Negative afterimage is a stimulus which elicits a positive image. In order to experience this, one can look at a bright source of light and then look away to a dark area. The way negative afterimage works is when the eye's photo-receptors which are the rods and cones adapt to over stimulation and lose sensitivity. The photo-receptors which are constantly exposed to the same stimulus will fatigue their supply of photo pigment, resulting a decrease in signal to the brain. The way negative afterimage connects to perception is because of bottom up processing where the stimulus influences what we perceive. https://www.youtube.com/watch?v=szy8iNCljlQ <Link to the video

Illusions that Confuse Multiple Senses

In this video, several illusions are shown that deceive your senses. Illusions such as the Zöllner Illusion and the Poggendorff illusion confuse our bottom up processing by tricking our vision. However, our vision isn't the only sense that these illusions can confuse, blind individuals presented with raised versions of the same illusions are also confused by them. These illusions effect the visual and touch systems by confusing our bottom up processing by tricking out sight and touch. https://www.youtube.com/watch?v=Je1mkzRU5rc&t=64s

The Rotating Mask Illusion- Schizophrenia

A schizophrenic process is more of a bottom up process than a top down which is what we do. We are unable to see a hollow face at first because we have never seen that before in our prior experience. This illusion occurs because the brain interprets information based on context and previous experience, or top down processing. In schizophrenic people there is a dysconnectivity between the parietal cortex, where top down occurs, and the lateral occipital cortex, where bottom up occurs, which is why they see the hollow face right away. In healthy people the connectivity in these areas are increased which is why they see a regular rotating face

Philosophy of Perception

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