Auditory Cognition
Auditory Perception and Short-Term Memory
In order to form a stable percept of the world around us it is necessary to monitor constant changes that arise in the perceptual scene. The meaning of sounds develops over time and in order to integrate and interpret different auditory signals it is therefore often necessary to store information in short-term memory. The mechanisms by which perceptual information is stored over such short periods of time, however, have puzzled scientists across disciplines and how and to what extent early sensory regions are involved in the maintenance of auditory memories remained unclear. I investigate how physical and semantic features of simple and naturalistic, non-verbal sounds are encoded in auditory cortex and whether auditory information is processed in a similar way during perception and higher-level cognitive processes such as auditory short-term memory and imagery.
Remembering by Imagining?
It is often assumed that maintaining information in short-term memory is a form of imagery and that both processes recruit early sensory regions (e.g. Hubbart, 2010; Pasternak, & Greenlee, 2005). When remembering your favourite song it might indeed help imagining it in your head repeatedly but while listening to your favourite song (and forming an integrated and pleasant perception thereof by storing the previous seconds in short-term memory) constant rehearsal through imagery does not seem very feasible. Using change detection and imagery tasks, we found that auditory perception, short-term memory and imagery do not rely on the same neural mechanisms. When information has to be kept in memory for short periods of time, we observe stimulus-specific suppression of auditory cortex which seems to protect information in short-term memory from being overwritten by potentially interfering sounds and/or might serve as a predictive coding mechanism that can signal whether a change has occurred. Auditory imagery on the other hand does activate similar auditory regions as those involved during the perception of complex sounds. Auditory short-term memory, thus, seems to operate fairly automatically and does not simply re-activate areas recruited during perception as could have been assumed based on similar studies in vision (for a review see Linden, 2007; Pasternak & Greenlee, 2005) and is different from imagery during which sound is voluntarily and actively generated in one’s mind.
Improving Memory by improving Encoding
Drawing upon the variability in performance in these tasks, we furthermore investigate whether the precision with which features are encoded and maintained in short-memory determines individual differences in change detection. Like in vision (see above), our results indicate that how information is encoded determines auditory short-term memory capacity. Interestingly, individuals who use an imagery strategy while having to maintain information in short-term memory do not show improved performance, again supporting the hypothesis that it is possible to detect changes in auditory information without much effort.