Making sense of ourselves
Making sense of ourselves

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

Making sense of ourselves

3.3 Rotating snakes illusion

Visual illusions demonstrate the differences between peripheral and foveal vision. In this ‘rotating snakes’ example, the circles appear to be moving. In fact, this is just a static image. If you fixate on the centre of one of the circles, it will stop moving.

Activity 6 Rotating snakes illusion

Described image
Figure 4 Rotating snakes illusion

Why might this be the case? Note down what you think might cause this illusion, or any thoughts you have on your experience of it.

You can type text here, but this facility requires a free OU account. Sign in or register.
Interactive feature not available in single page view (see it in standard view).

Discussion

When you view the image, your peripheral vision produces the sensation of movement. When you fixate, and use foveal vision, the motion stops. Our peripheral visual fields are specialised for motion detection, whereas our central (foveal) vision is specialised for colour and detail. The direction that the wheels move in, and the strength of the effect, are dependent on the background luminance. When presented on a bright white background, the wheels appear to move more slowly than when presented on a grey background. The motion experienced by most people viewing this example is believed to come from the arrangement of the components of the ‘snakes’. These cause asymmetric luminance steps, which in turn trigger motion detectors, allowing us to perceive the static image as moving.

DE200_4

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to university level study, find out more about the types of qualifications we offer, including our entry level Access courses and Certificates.

Not ready for University study then browse over 900 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus