Masters Theses

Date of Award

6-1984

Degree Type

Thesis

Degree Name

Master of Arts

Major

Audiology

Major Professor

Allan O. Diefendorf

Committee Members

Deborah Arthur, Samuel B. Burchfield, David M. Lipscomb

Abstract

The past decade of infant auditory research has generated new empirical and methodological insight. Studies have compared the sensory capabilities of infants and adults on various auditory measures; however, at present there are no studies on intensity discrimination. The purpose of this study was to compare the just noticeable difference (jnd) for intensity in normally hearing infants and adults.

Eight infants were tested using an adaptation of the Visual Reinforcement Audiometry (VRA) paradigm. Subjects were trained to head-turn for the correct detection of an intensity increment between 1 dB and 10 dB. A correct head-turn response was reinforced by activating an animated mechanical toy in a plexiglass box. The jnd was determined for each subject at 20 dB and 70 dB HTL carrier tones of 1000 Hz. A bracketing procedure was utilized and the criterion measure was three correct increment discriminations at the same level. Eight adult subjects were tested by raising their hand when they detected an increment. The same stimulus parameters and response criterion were used.

The results of this study indicate that intensity discrimination can be assessed reliably in both populations. While infants required a greater intensity change before detecting increments than adults, the jnd was smaller at 70 dB HTL than at 20 dB HTL for both groups. Statistical analysis revealed significant differences between jnds at 20 dB HTL and 70 dB HTL for both infants and adults. In addition, significant differences were found between infant and adult jnds at each presentation level.

The difference in the jnd between the adults and infants may reflect maturation of the auditory system; however, other factors such as attention, motivation, cognition and infant state may contribute to the observed differences. While there was a quantitative difference between groups, infants and adults were qualitatively similar in the processing of intensity information.

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