A psychophysical investigation of human visual perceptual memory. A study of the retention of colour, spatial frequency and motion visual information by human visual short term memory mechanisms.

摘要

The aim of this thesis was to investigate how visual information is organised inudperceptual short term memory, with special interest in colour, spatial frequencyudand velocity. Previous studies of VSTM have indicated the existence of specificudmemory mechanisms for visual attributes such as orientation, spatial frequency,udvelocity, contrast and colour. The retention of information in visual short termudmemory for these basic visual attributes can be disrupted by the presentation ofudmasking stimuli during inter-stimulus intervals (ISIs), which are outside theudrange of traditional sensory masking. We exploited this memory masking effectudin order to examine the organisation of visual information in VSTM. Four groupsudof experiments were conducted in which participants carried out a delayeduddiscrimination paradigm that employed a two-alternative forced choice (2-AFC)udprocedure in conjunction with a method of constant stimuli. The fidelity of VSTMudwas measured by performance markers such as discrimination thresholds andudpoint of subjective equalities. We have found selective memory masking effects,udwhich serve as further evidence in favour of the modular organisation in VSTM,udnamely, that human visual perceptual memory is based upon multiple, tunedudchannels in case of colour, spatial frequency and speed, similar to those foundudin the earliest stages of visual processing for spatial frequency. Moreover, eachudof these storage mechanisms are tuned to a relatively narrow range of stimulusudparameters that are closely linked to visual discrimination mechanisms. Theseudfindings add further support to the view that low-level sensory processingudmechanisms form the basis for the retention of colour, spatial frequency andudvelocity information in perceptual memory. We also found evidence for theudbroad range of transfer of memory masking effects across spatial location,udwhich indicates more long range, long duration interactions between channelsudthat are likely to rely upon contributions from neural processes located in higherudvisual areas. In conclusion, the experiments presented in this thesis provideudsignificant insight into the organization of visual information in perceptual shortudterm memory.