Integration of localisation and width
As discussed previously
the model requires the predictions of the perceived location and width of the sound to be combined to accurately predict the overall perceived width of the sound across a range of frequencies. The first step in this was to convert the IACC to a pair of ITD values that denote the positions of the left and right edges of the sounds. This was undertaken by conducting a series of experiments to determine an equation to convert from the IACC value to a pair of ITD values.
It is commonly believed that the ITD affects the perceived location and the IACC affects the perceived width of a sound, with no interaction. We conducted a number of experiments to investigate the effect of combinations of various values of IACC and ITD on the perceived location and width of sounds and found that there is in fact a significant interaction between these factors [Mason et al 2004d
]. The IACC can affect the perceived location of a sound, in that a signal with a low interaural correlation is perceived to be almost central even when it has a large interaural time difference. In addition, large ITD values can cause stimuli of mid to high frequencies to have multiple peaks across the range of τ of ±1ms. Methods were derived to compensate for these factors, and these have been included in the algorithm that combines the width and location results.
The data are then output in terms of an ITD for conversion to a more perceptually relevant and intuitive scale.