Visual processing of multielement arrays and the selective masking function

Keating, John Kevin (1977) Visual processing of multielement arrays and the selective masking function. Masters thesis, Memorial University of Newfoundland.

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Abstract

If a visually presented array of alphanumeric material is followed by a patterned masking stimulus the perception of the items at the ends of the display will be unaffected, while those in the centre of the array will be masked substantially. Termed selective masking, this phenomenon has been extensively investigated, largely as a technique to make inferences about the nature of visual information processing. -- The results of numerous studies on the selective masking phenomenon indicate that the items at the ends of a row are processed first and thus escape the effect of a temporally following mask. There has been some uncertainty about the order of processing after the end items have been processed. Experiment I investigated this processing order by systematically varying the interval between the offset of the letter arrays and the onset of the masking stimulus. The results indicated that the ends of the row are indeed processed first and that subsequent serial processing is in general from both ends towards the middle. -- It has also been shown that this ends-middle processing order can be altered if the observer is given sufficient information to direct his attention to a single item in the display. When a spatial cue is presented for one of the items at stimulus onset or when the subject is instructed to report an item which differs in category from the background items, the subject attends to a single item and therefore does not process the array with an ends-first approach. The second experiment investigated the extent and nature of the processing strategy which observers use when presented with an array containing six letters and one digit. In addition, the effect of a categorically incongruous item on the processing of background items was studied. The results show that observers do not selectively process the incongruous item when digit report is required on only a small portion of the trials. The data also indicate that the processing of the odd item and the background items occurs at the same time, i.e. in parallel, but that the overriding serial, ends-first processing strategy common to encoding a multielement array is still employed.

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