The Effect of Noise on Memory for Spoken Syllables

The effects of auditory and visual presentation upon short-term retention of verbal stimuli are reviewed, and a model of the structure of short-term memory is presented. The main assumption of the model is that verbal information presented to the auditory and visual modalities is processed in separate streams that have different properties and capabilities. Auditory items are automatically encoded in both the A (acoustic) code, which, in the absence of subsequent input, can be maintained for some time without deliberate allocation of attention, and a P (phonological) code. Visual items are retained in both the P code and a visual code. Within the auditory stream, successive items are strongly associated; in contrast, in the visual modality, it is simultaneously presented items that are strongly associated. These assumptions about the structure of short-term verbal memory are shown to account for many of the observed effect of presentation modality.

All 10 forms of the test of Speech Perception in Noise (SPIN) were presented to 128 listeners who had some degree of sensorineural hearing loss. Presentation of the speech track was at 50 dB above the estimated threshold for the babble track. Signal-to-babble ratio was 8 dB. Half of the subjects listened through headphones and half via loudspeaker. Half were tested in a single session and half in two sessions spaced 2-4 weeks apart. Two markers independently scored every test session. Statistical analyses indicate that transducer, number of visits, and order of test form presentation have little or no effect on test scores, and differences between markers, although significant, are quite small. The subtests consisting of items with strong contextual cues generate an average reliability coefficient of .91, whereas the value for the low-context subtests is .85. The 10 forms do not, however, constitute a set of equivalent forms, and there are large differences in mean performance on the low-context portions.