Top-down and bottom-up interaction: manipulating the dichotic listening ear advantage.

The aim of the study was to investigate interactions between top-down and bottom-up information processing in the auditory domain. For this purpose, thirty-five right-handed participants with normal hearing acuity were tested with consonant-vowel dichotic stimulus pairs. Bottom-up stimulus characteristics were manipulated by gradually varying interaural intensity difference from -21 dB in favor of the left ear to +21 dB in favor of the right ear (including a no difference baseline condition). Top-down manipulation consisted of three conditions with different attention instructions: one free report condition, and each one condition requiring the participants to focus their attention on the right ear and on the left ear, respectively. The results showed a significant interaction of bottom-up and top-down manipulations with respect to the modulation of the ear advantage. Post-hoc analysis showed that the effect of directing attention was reduced when the intensity difference favored the to-be-attended ear. Thus, bottom-up intensity and top-down attention manipulations should not be regarded as independent but rather interacting factors when it comes to the manipulation of the ear advantage in a dichotic listening situation.