Factors Limiting Performance in a Multitone Intensity-Discrimination Task: Disentangling Non-Optimal Decision Weights and Increased Internal Noise

Daniel Oberfeld,Walt Jesteadt,Martha Kuta,Warren H Meck

doi:10.1371/journal.pone.0079830

Daniel Oberfeld, Walt Jesteadt + Show 2 more

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https://doi.org/10.1371/journal.pone.0079830

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Abstract

To identify factors limiting performance in multitone intensity discrimination, we presented sequences of five pure tones alternating in level between loud (85 dB SPL) and soft (30, 55, or 80 dB SPL). In the “overall-intensity task”, listeners detected a level increment on all of the five tones. In the “masking task”, the level increment was imposed only on the soft tones, rendering the soft tones targets and loud tones task-irrelevant maskers. Decision weights quantifying the importance of the five tone levels for the decision were estimated using methods of molecular psychophysics. Compatible with previous studies, listeners placed higher weights on the loud tones than on the soft tones in the overall-intensity condition. In the masking task, the decisions were systematically influenced by the to-be-ignored loud tones (maskers). Using a maximum-likelihood technique, we estimated the internal noise variance and tested whether the internal noise was higher in the alternating-level five-tone sequences than in sequences presenting only the soft or only the loud tones. For the overall-intensity task, we found no evidence for increased internal noise, but listeners applied suboptimal decision weights. These results are compatible with the hypothesis that the presence of the loud tones does not impair the precision of the representation of the intensity of the soft tones available at the decision stage, but that this information is not used in an optimal fashion due to a difficulty in attending to the soft tones. For the masking task, in some cases our data indicated an increase in internal noise. Additionally, listeners applied suboptimal decision weights. The maximum-likelihood analyses we developed should also be useful for other tasks or other sensory modalities.

Highlights

In experiments on multitone intensity discrimination, the stimulus consists of several sequentially presented elements and the task is to judge the intensity of this multitone stimulus (e.g., [1,2])
Decision Weights Before reporting the statistical analyses, we describe the pattern of average normalized decision weights for the overall-intensity task and the masking task
Compatible with the results by Lutfi and Jesteadt [7], the weights assigned to the loud tones were much higher than the weights assigned to the soft tones at the two lower mean levels of the soft tones

Summary

Introduction

In experiments on multitone intensity discrimination ( termed multitone pattern discrimination), the stimulus consists of several sequentially presented elements and the task is to judge the intensity of this multitone stimulus (e.g., [1,2]). The listeners placed much higher weight on the loud tones than on the soft tones, even if the level information from the soft tones was rendered more reliable by presenting a larger level increment on the soft than on the loud tones. This pattern of weights is consistent with other reports of a ‘‘level dominance’’ effect [8,9]. For sounds beginning with a gradual decrease in level, on the other hand, the first part of the sound receives the highest weight [5] Both observations are compatible with attention to the loudest elements [8]. Lutfi and Jesteadt interpreted these data as to showing that the spectral difference between soft and loud sounds facilitated the direction of attention to the soft elements

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