Forgetting in visual working memory: Internal noise explains decay of feature representations.

The precision of visual working memory (VWM) representations decreases as time passes. It is often assumed that VWM decay is random and caused by internal noise accumulation. However, forgetting in VWM could occur systematically, such that some features deteriorate more rapidly than others. There exist only a few studies testing these two models of forgetting, with conflicting results. Here, decay of features in VWM was thoroughly tested using signal detection theory methods: psychophysical classification images, internal noise estimation, and receiver operant characteristic (ROC). A modified same-different memory task was employed with two retention times (500 and 4000 ms). Experiment 1 investigated VWM decay using a compound grating memory task, and Experiment 2 tested shape memory using radial frequency patterns. Memory performance dropped some 15% with increasing retention time in both experiments. Interestingly, classification images showed virtually indistinguishable weighting of stimulus features at both retention times, suggesting that VWM decay is not feature specific. Instead, we found a 77% increase in stimulus-independent internal noise at the longer retention time. Finally, the slope of the ROC curve plotted as z-scores was shallower at the longer retention time, indicating that the amount of stimulus-independent internal noise increased. Together these findings provide strong support for the idea that VWM decay does not result from a systematic loss of some stimulus features but instead is caused by uniformly increasing random internal noise.

Annoyance, perception, and physiological effects of wind turbine infrasound.

Even though some individuals subjectively associate various symptoms with infrasound, there are very few systematic studies on the contribution of infrasound to the perception, annoyance, and physiological reactions elicited by wind turbine sound. In this study, sound samples were selected among long-term measurement data from wind power plant and residential areas, both indoors and outdoors, and used in laboratory experiments. In the experiments, the detectability and annoyance of both inaudible and audible characteristics of wind turbine noise were determined, as well as autonomic nervous system responses: heart rate, heart rate variability, and skin conductance response. The participants were divided into two groups based on whether they reported experiencing wind turbine infrasound related symptoms or not. The participants did not detect infrasonic contents of wind turbine noise. The presence of infrasound had no influence on the reported annoyance nor the measured autonomic nervous system responses. No differences were observed between the two groups. These findings suggest that the levels of infrasound in the current study did not affect perception and annoyance or autonomic nervous system responses, even though the experimental conditions corresponded acoustically to real wind power plant areas.