Effects of irrelevant level fluctuation on frequency discrimination by young and older adults

Blas Espinoza-Varas, Hyunsook Jang
2005 Acoustical Science and Technology  
Introduction The present experiments assessed effects of irrelevant fluctuation in signal level on frequency discrimination thresholds (FDTs) of young and older adults; more generally, age effects on the ability to ignore irrelevant auditory information were studied in psychoacoustic discrimination tasks. Previous research suggests that this ability degrades with aging, and that performance decrements induced by irrelevant auditory information are more severe in older than in young adults [1]
more » ... young adults [1] [2] [3] . However, most of the evidence comes from studies using speech-recognition tasks; frequency discrimination tasks with simple sinusoids have not been employed thus far. In order to convey irrelevant information, the auditory display must include two or more sources of discernible information. In addition, the sources must provide conflicting information so that, to respond correctly, subjects must succeed both at attending to one (relevant) source and at ignoring the other (irrelevant) sources. That is, subjects must be able to extricate relevant and irrelevant information at the perceptual level. The mere addition of noise, stimulus context or variability does not necessarily create irrelevant information; to do so, systematic stimulus differences that are discernible yet inconsistent with relevant information must be displayed also [4, 5] . In two-interval, two-alternative, forced-choice (2IAFC) frequency discrimination tasks, irrelevant information can be engendered by fluctuation in the signal level, either within trials, between trials, or both [6, 7] . Previous research shows that such random fluctuation has only small effects in the FDTs of well-trained young adults; compared to the fixed level condition, Weber fractions increase by a factor of 2.7 on average. That is, young adults have little difficulty ignoring random irrelevant level fluctuation in 2IAFC frequencydiscrimination tasks. In the present study, a modification of the above paradigm was used to compare the ability to ignore irrelevant auditory information of young and older adults; in both groups, FDTs were measured with and without fluctuation in signal level. The effects of level-fluctuation polarity (positive or negative) and training were also studied. Because target information always consisted of positive frequency increments, it was assumed that the positive irrelevant level differences would be harder to ignore than the negative, owing to similarity and
doi:10.1250/ast.26.394 fatcat:i3kqkhnw3rdhdcvh27lvpzxpa4