Available online
Description
The programme examines visual illusions and what these can tell researchers about normal processes of perception.
The programme examines visual illusions and what these can tell researchers about normal processes of perception.
| Module code and title: | SD286, "Biology, brain and behaviour" |
|---|---|
| Item code: | SD286; 12 |
| First transmission date: | 12-09-1981 |
| Published: | 1981 |
| Rights Statement: | |
| Restrictions on use: | |
| Duration: | 00:24:00 |
| + Show more... | |
| Producer: | Jenny Hughes |
| Contributor: | Ilona Roth |
| Publisher: | BBC Open University |
| Keyword(s): | Cognition; Hermann grid; Physiology; Visual illusions |
| Footage description: | Ilona Roth introduces the programme. She shows an illusion which looks like a Union Jack and then steps into a 'Tardis' which disappears from the studio. A common illusion, without which colour television would not be possible, is discussed and demonstrated. Ilona Roth identifies the 'flicker fusion frequency' and the trichromatic colour system, the basis for creating the illusion of movementand colour on television. Another illusion, based on a white grid pattern over a black background, is shown. Here the intersections of the white grid lines are normally seen as containing dark grey areas. With the aid of animated diagrams, Ilona Roth explains this illusion in terms of a 'receptive field' in the visual ganglions. Viewers are asked to concentrate on a grating which appears on the screen. The grating is tilted to the left. After a period the grating is changed to the vertical position but the viewer appears to see it tilted to the right. Ilona Roth points out the importance of orientation in the visual system and explains the illusion in terms of orientation sensitive cells in the visual system. Animated diagrams help to illustrate her points. Viewers are asked to undergo another illusion experiment. This one is designed to show that the human visual system is not only orientation sensitive but is also sensitive to particular colours. Ilona explains that certain cells require both dimensions for activation. The effect experienced by viewers is known as the McCullough Effect. Ilona Roth goes on to look at illusions which depend on a cognitive interpretation by the visual system rather than the simple neuro-anatomical level as in the above illusions. Shots of an illusion which looks like two triangles with circles at the points. She explains that the visual system tries to interpret what it sees in the light of past experience and that it is sometimes confused, hence the illusion. Shots of three other illusions, out-of-focus car lights, a Johanson spot demonstration and a diagram which depends on fluctuating perception. As an analogy to a visual system confused by unfamiliar data, a scientific parallel is shown using clips from a Dimbleby Talk-In programme in which Uri Geller bends spoons. Ilona Roth goes on to show several more illusions in which the visual system is led astray through errors in interpretation. Shots of a hollow mask, a broken triangle and two lines of equal length drawn across two converging lines. Ilona Roth summarises the programme. |
| Master spool number: | HOU3595 |
| Production number: | FOUS183N |
| Videofinder number: | 2084 |
| Available to public: | no |
