## 1 Introduction  
The localization of sound sources plays a crucial role in animal behavior, and it is also a very important function for humans. Detecting sound source direction in horizontal plane is based on the disparities in time and the intensity of the sound reaching both ears, namely interaural time difference (ITD) and level differences (ILD) which are assumed to be responsible for sound lateralization in low and high frequencies, respectively [1]. This frequency-based behavioral dichotomy, which is known as the duplex theory of sound lateralization, has a physio-anatomical counterpart in the brain as is briefly explained below. Studies conducted on the hearing system suggest that ITD and ILD cues to sound lateralization are processed in the medial superior olive (MSO) and the lateral superior olive (LSO) sub-rulei of the superior olivary complex (SOC) located in the brainstem, respectively. However, there is some debate about the roles and neural mechanisms of these nuclei in mammalian sound lateralization [2]. The impulses from the cochlear nucleus ipsilateral to the ear are considered to go directly to the ipsilateral LSO. These impulses provide excitatory input to the neurons of ipsilateral LSO and send inhibitory impulses to the contralateral LSO via inhibitory interneurons in the medial nucleus of the trapezoid body (MNTB) [2]. This process provides the nucleus a neural mechanism capable of encoding interaural intensity differences [3]. On the other hand, the MSO receives excitatory inputs directly from both ipsi- and contra-lateral cochlear nuclei. Meanwhile, a neural network forms axonal delay lines that travel in opposite directions over the impulses from the two ears [4]. Such an arrangement makes the nucleus a neural mechanism capable of encoding interaural time differences as hypothesized by _[PERSON]_ in his classical model [5]. In addition to this histo-anatomical arrangement, there exists a tonotopic organization in the auditory system of the brain so much so that the neurons display selectivity to the frequency of the stimulating sound. Interestingly, most LSO units that produce discharge rates related to interaural level difference are mostly responsive to sounds with high frequencies [2; 6]. On the other hand, the majority of the units in MSO, which achieves the place-coding of interaural time differences, are most responsive to sounds with low frequencies [2]. This appears to be a physio-anatomical compliance of the auditory brain with the physics of the acoustical environment, which reveals itself as the frequency-dependent weights of ITD and ILD in sound lateralization as expressed by duplex theory [7]. This theory describes the complementary roles of ITD and ILD cues in the lateralization of pure tones at low and high frequencies, respectively. While the acoustic shadowing of the head is negligible for low-frequency sounds, it is quite large for the sounds at high frequencies. This results in the ILD assuming a dominant role in the lateralization of high-pitched sounds [1; 8; 9]. There is indeed a vast amount of information in the literature about the coding of the ITD and ILD cues in auditory nuclei of the brainstem and tegmentum in avaians and vertebrates. However, how these two pieces of information are combined in the higher centers of the brain and cortex still remains to be explained and modeled. The present modelling study using a communications approach based on the measured psychophysical error-rate data is an attempt in this direction. Sound localization in humans has been studied intensively for several years. Some of the studies [9; 10; 11; 12; 13] focused on trading between ITD and ILD cues by adjusting these cues to produce a centered acoustic image that gives the point of equivalence between the cues, and the ratio of ITD to ILD in that situation gives the ITD/ILD trading ratio using single-frequency tones. The frequency-based behavioral dichotomy which is known as the duplex theory of sound lateralization is a simplification.