Perceptual Cycle Research Articles

Direct theory of perception : an évaluation by représentatives of indirect théories of perception

Summary : Direct theory of perception Gibson's theory has generated a lot of discussion with indirect theories of perception. But how do representatives of these theories evaluate Gibson's ecological approach? In this article an attempt is made to provide an answer to this question. The very diverse reactions are split up into two large groups: Criticisms and reconciliation attempts. The criticisms stress the need for compulational and representational processes. Four kinds of reconciliation attempts are distinguished: (1) Changing stimulus patterns and decoding principles, (2) direct information pickup as part of a perceptual cycle, (3) not all perception is direct, and (4) direct perception as preattentive processing. Key-words : direct perception, representation, computation.

Selective looking and the noticing of unexpected events.

Subjects in a selective-looking paradigm (Neisser & Becklen, 1975) attended to one of two visually superimposed videotaped ballgames by responding every time the ball was passed in the target game. An unexpected, yet highly visually conspicuous, event, occurring about halfway through the l-rain game sequence, was noticed by only 18 of 85 subjects. Noticing was unrelated to the delay between the event and the posttrial inquiry, and explicit “iconic” instructions to describe the last image seen immediately after interruption proved ineffective in enhancing noticing rates, despite optimal visual conditions). Instead, noticing appeared to be related to the specific anticipatory possibilities within the attended sequence itself. Content analysis indicated that the latter part of the unexpected event sequence afforded greater anticipatory opportunities, and the findings suggested that noticers who were skilled at the main task were more likely to detect the event during this part, whereas unskilled noticers showed no such pattern. Results were consistent with and interpreted in terms of Neisser’s (1976) notion of the “perceptual cycle.”

Scanning mechanisms and the EEG

High beta activity (21 to 33 c/sec) was found to increase during unstructured stimuli. Such activity was regarded as a correlate of an internal scanning mechanism. Upon reduction of alpha activity consonant with onset of stimulation, beta activity increased in the temporal areas for all stimuli studied. This increase was also observed in the occipital areas for a diffused vision condition and in the prefrontal areas for a condition in which the subject was required to listen to white noise. Beta activity increase in the prefrontal areas also occured while listening to a story and while performing mental arithmetic. It was concluded that beta activity increased as long as a condition existed in which the stimulus, whether internal or external, required structuring activity on the part of the organism. According to this rationale there is a hierarchy of scanning mechanisms beginning with alpha activity (that can be thought of as scanning for any stimulation); its function ceases or subsides in the presence of a broad range of percepts, whether internal or external. At this point in the perceptual cycle, faster scanning mechanisms occur, such as beta activity in the temporal areas. The latter can be thought of as scanning for structure. This activity subsides just as alpha activity does when the conditions for its existence are no longer present. Beta activity disappears when the stimulus has acquired the necessary structure. It is not unlikely that faster mechanisms may be present to mediate even more complex internal processes. This investigation was possible via computer analysis of 16 EEG areas digitized and stored on computer tape at the time of data acquisition. The changes observed were derived from autospectra values for 8-sec periods of 16 frequency bands from 1 to 33 c/sec, obtained under various conditions of stimulation.