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3. PERCEPTION
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3.1 Recognition and Tactical Decision under Varying Conditions (Project No. 5)
3.1.1 Colour Coding of Tracks in Coloured Noise (Edwards, Poulton)
The tracks of submarines can be coded by colour to indicate their direction and speed. Poulton and Edwards found that this does not increase the time taken to detect them, provided they are not camouflaged by sea noise. When camouflaged however, colour is a disadvantage unless the person knows the colour for which to search (176).
3.1.2 Detection of Targets with Computer Assistance (Murrell)
In noisy visual displays the targets are not always the most conspicuous signals. An automated detection system may be able to use additional cues, which are not available in the visual display presented to the man. Detection was shown by Murrell to be most efficient if the information in the visual display is combined with the information which is extracted automatically (140)- Naval ratings can combine the information from the two sources, but they perform less well than an ideal observer. In order to combine the information from two sources most effectively, people need to be trained to understand how the sources are related to each other ( 141).
3.1.3 Person Recognition (Baddeley, Bruce, K. Patterson, D.C.V. Simmonds, Woodhead)
Attention so far has concentrated primarily on faces. Evaluation by Woodhe.id, Baddeley and Simmonds (212) of an ongoing scheme designed to train fa-e recognition showed it to be ineffective. This may have been because of the emphasis on teaching the categorisation of individual features, an approach which Patterson and Baddeley (145) find to be less effective for subsequent recognition than requiring categorisation on more general"personality"characteristics of the face. The latter study also examined the role of disguise, and showed that a change in hair style and the addition or removal of a beard produced large and consistent decrements iu recognition performance. Some current work by Patterson i3 utilising film, and showing for example that if original learning has occurred from films of whole moving persons, tests on static photogxaphs of faces produce rather poor recognition performance. Such results have implications for procedures of eyewitness testimony. At a more theoretical level, Bruce (34) has studied the process of recognising familiar faces, using the faces of politicians and television personalities and has shown that when several faces are being searched for. both their visual and semantic characteristics (e.g. politician or TV) are utilized simultaneously in reaching a decision.
3.2 Triggering Mechanisms in Photosensitive Epilepsy (Wilkins)(Project No. 2)
Two independent series of experiments by Wilkins, one at Runwell Hospital and one at Addenbrooke's Hospital, have established that a substantial proportion of photosensitive patients are sensitive not only to flicker but also to pattern (45; 184; 189). Gratings with a spatial frequency of 2 cycles/degree have been found to be optimal for inducing paroxysmal EEG activity, every patient's individual optimum lying within one octave of this value. The probability of paroxysmal activity has been found to increase with pattern subtense, individual patients requiring markedly different pattern sizes to induce paroxysmal activity with a given probability. The findings obtained by Wilkins et al (189) with a single pattern-sensitive patient have now been replicated and extended on further patients. In general, the characteristics of visual stimuli to which patients are sensitive are quite consistent with a seizure trigger in the striate cortex (192).
Optical treatment using spectacles with one lens frosted has now been found to be highly effective in three severe cases (190). Treatment with dark glasses is currently under investigation and initial indications are that it may have a more limited effectiveness. A substantial proportion of photosensitive patients are sensitive to television (184) and prevention of TV-induced attacks using polarised spectacles and a polarised screen over the TV (186; 188; 190) has achieved some success.
3.3 Noise Disruption of Auditory Processing (Barton, Johnson-Davies, Milroy, Nimmo—Smith, R. Patterson)(Project No. 22)
Designers of auditory warnings and sound transmission systems often ask us "How can we ensure that the signal the listener is intended to hear will be audible in the environment for which it is intended?" At present, to answer this question auditory threshold is determined by reproducing the particular environment in the laboratory as accurately as possible and measuring threshold for a group of observers in that environment - a time-consuming and costly process. Consequently Patterson et al (148; 150; 153; 154) have been investigating auditory masking and using the results of this research to develop a general model of masked threshold. The heart of the model is the auditory filter which it is assumed the listener centres on the signal to filter out background noise and so improve the detectability of the signal.
More recently efforts have centred on attempts to generalise the concept of the auditory filter to other areas of psychoacoustics. The chief alternative method to the auditory filter for specifying the frequency discrimination ability of humans is the psychophysical tuning-curve. Patterson and Johnson-Davies have embarked on a project to show that these two concepts - the auditory filter and psychophysical tuning-curves -are two sides of a single coin, but that the auditory filter concept holds more promise because more progress has been made on quantification (151; 152).
3.4 The Design and Evaluation of Auditory Warning Systems (Barton, Johnson-Davies, Milroy, Nimmo-Sraith, R. Patterson, Piatt) (Project No. 21)
Auditory warnings have the distinct advantage that they will alert an operator irrespective of where he is looking. The sound source can thus be located in an otherwise unusable portion of a console or dashboard. As a result auditory warnings are being used in ever increasing numbers. Unfortunately they are often designed without due regard for the environment in which they are to be used - sometimes they are not even audible. On this project we evaluate auditory warnings and establish guidelines for their design.
At the request of the Chemical Defence Establishment an auditory warning intended for use on a chemical detector was evaluated. The warning proved inaudible in the intended environment and its frequency characteristic was unsuitably narrow. We provided guidelines for a preferred warning sound, the manufacturer produced an improved warning which upon evaluation proved satisfactory (149).
Operational pilots flying civil aircraft with a relatively large number of auditory warnings make a small proportion of errors when asked to identify tape-recordings of the warnings in their aircraft. In stage 1 of a project initiated by the Civil Aviation Authority in March 1977 we are recording the warnings while the aircraft are flying and attempting to determine whether the observed confusions are inherent in the existing warning sounds or whether the situation could be alleviated with the use of a short training tape. In stage 2 of this project, now beginning, we will attempt to create a set of confusion resistant non-verbal auditory warnings for use in civil aircraft. They will be tested against existing warnings and verbal warnings.
What distinguishes speech, auditory warnings, and music from noise is that their waveforms are repetitious and so produce one or more pitch perceptions. The design of a distinctive set of auditory warnings that do not interfere with each other when they occur simultaneously requires an understanding of human pitch perception. Recent research by Patterson, Johnson-Davies and Milroy has confirmed a long established suspicion that the auditory mechanism for extracting the pitch of complex waves is more similar to an autocorrelator than to a spectral analyser as previously assumed. Our research supporting this view has been reported in a number of journal articles and a book chapter (148; 150; 151; 152; 153; 154).
3.5 Improved Methods of Audiometric Assessment and Design of Hearing Aids (R. Patterson, Milroy)(Project No. 3)
The standard hearing test, the audiogram, provides only the most gross prediction of speech intelligibility. It tends to reveal damage only after significant damage has occurred. Recently a number of investigators have measured the shape of the auditory filter which describes the frequency selectivity of the car and, as such, represents the basic discriminative power of the ear. Most of the work was done on normal hearing subjects but there is some data on patients with hearing disorders which indicates that they have less exacting filter shapes than normals. Thus we have begun a project to produce and assess a clinical test for auditory filter shape which, it is hoped, will measure factors more relevant to speech perception, and detect hearing loss at an earlier stage so that corrective action can begin before gross damage occurs.
An experiment to estimate auditory filter shape, that can be run in 15 minutes on groups of hearing impaired patients or normals, has been designed and the component parts assembled. Further progress awaits the establishment by the new Institute of Hearing Research of a network of clinics, where patients can be tested in greater numbers.