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Topics in Computerised Visual Stimulus Generation

Topics in Computerised Visual Stimulus Generation by Tom Robson is published as a chapter of Vision Research, A Practical Guide to Laboratory Methods, edited by Roger Carpenter and John Robson, OUP 1998.


4. Tips and Tricks
4.2 temporal

Techniques for increasing temporal resolution are exactly analogous to those that can be used for increasing spatial resolution. For example, consider presenting a stimulus to an observer by turning it full-on on one frame of the display, leaving at the desired luminance for 10 frames and then turning it off again. If the display is operating with a 100Hz frame-rate this corresponds to viewing the stimulus through a 100ms square time window. As usual, the word square should be a warning that bandwidth limiting is not operating and that the frequency components of the underlying stimulus are liable to be modified when viewed in this way. The preferred technique in this case is to utilise available luminance resolution by viewing through something like a raised cosine or Gaussian window whereby the stimulus intensity is slowly increased from zero over several frames before reaching a plateau and then being ramped off again. The desired stimulus waveform should be seen as coming from a continuous function or a least a very long list of numbers which is subsequently sampled by the display process once per frame. In this way, the temporal resolution of the system is determined only by the available luminance resolution and the accuracy with which the function can be calculated and not by the display's frame-rate.

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