i,m currently doing an asignment and came accross tachistoscope need to know more about it!

-- teresa furey (teresa.furey@nuigalway.ie), January 16, 2002

Answers

"T-scopes" (as they are often nicknamed) are (well, *were*) used to display stimuli for very short periods of time (measured in hundredths or even thousandths of seconds). This kind of very short stimulus-presentation is now usually done on computer screens. They were a standard piece of experimental psychological equipment almost from the very beginning.

-- Christopher Green (christo@yorku.ca), January 17, 2002.

The problems faced by early vision researchers were to present visual stimuli for precisely controlled lengths of time and for times that might be very brief -- as Christopher Green says, for hundredths or even thousands of a second. It's easy to flash a very brief stimulus on a screen, but mush more difficult to know exactly how brief it was, and to make the next flash exactly .005 second (for example) longer.

Before computer controlled tachistoscopes, we used camera-like shutters mounted on the lenses of slide projectors. Before that, there were very clever apparatuses that didn't use electronic controls at all, but depended on moving a window of controllable size in front of a visual stimulus at a known speed, so that the stimulus would be exposed for a known length of time. One type of such a tachistoscope depended on a window falling on vertical tracks; another type used a window on a rotating wheel. The known speed of falling objects or the known speed of the rotating wheel allowed for precise calculation of the length of time the stimulus could be seen through the window.

-- Warren Street (warren@cwu.edu), January 18, 2002.

Contrary to what Christopher Green has said, tachistoscopes are most definitely used today, especially in the field of Market Research, and typically when researching packaging design. For this type of test a projector tachistoscope is employed: an electromagnetic shutter in front of a projector lens is activated by a control unit.

For example, a design company might produce two new designs for a shampoo. The manufacturer would wish to know whether one of the new designs is more eye-catching to the shopper than his current design.

The market research company will commission a photographer to shoot a series of slides which include the test product, together with a number of competing brands. All of the products wll be arranged to simulate a shop or supermarket display. In each slide the test item will move to a different position on the shelves and the competitve products will similarly move to different positions. In a number of slides in the series, the test item will not appear and a substitute inserted in its place. The series of slides is repeated for each of the new and current designs.

When the slides are projected, the respondent clicks a button on a remote keypad and the recognition time to find the test item is recorded. In this way it is possible to test the reaction times of the respondents to the different designs, and to determine which is the easiest to recognise. This type of research is known as a standout test.

In an alternative mode, the t-scope can be pre-set to display a slide for a selected period of time, usually in the range of 0.1 second to 4 or 5 seconds. This range has been determined to be the most practical when respondants are viewing the relatively complex designs of modern consumer packaging.

This is different to the 'speed reading' usage of some computer based t-scopes which operate at much faster speeds when only a single word is flashed.

At this point I must express an interest as a manufacturer of projector tachistoscopes!

Clive Bubley clive@bubley.com www.bubley.com/t-scopes

-- Clive Bubley (clive@bubley.co.uk), June 11, 2004.