Two paradigms are presented to investigate the facilitatory effect of spatial cueing on perception of the features of objects. In Chapter 2, performance was studied for continuous tracking of the positional and non-positional features of multiple objects. Observers attempted to report the last feature value of a queried object. The results demonstrated a progressive decline in the precision of the representation of tracked objects, for orientation, spatial period and position. The decline was apparent as the number of objects was increased from one to two to four, and occurred before previously suggested capacity limits based on a fixed number of objects. Responses were more similar to past states of the queried object than to its last state, that is to say that responses exhibited perceptual lags. For orientation, and particularly for spatial period, perceptual lags increased as more objects were added to the attentional load. Analyses of error patterns broken down by likely confidence in responses suggested a contribution from serial processing. Further support for the notion that the lags were contributed to by serial processing, was suggested by two double report experiments presented in Chapter 3. Here, for spatial period tracking, processing appeared not to proceed purely in parallel. Why tracking performance may differ between features is discussed. Four experiments in Chapter 4 rule out the possibilities that the differences in lags between orientation and spatial period were due to artefacts relating to the range of feature values. Chapter 6 is an investigation into the benefits of attention in terms of noise reduction and sampling. Pre-cueing and dual task manipulations were used to compare the effects of attention with those of crowding, which has been demonstrated to increase internal noise. Spatially directed attention was found to reduce internal noise, consistent with the precision results of the previous chapters.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:584198 |
| Date | January 2007 |
| Creators | Howard, Christina J. |
| Publisher | Cardiff University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://orca.cf.ac.uk/55714/ |
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