The role of contingency and gaze direction in the emergence of social referencing

The current study assessed the importance of infant detection of contingency and head and eye gaze direction in the emergence of social referencing. Five- to six-month-old infants' detection of affect-object relations and subsequent manual preferences for objects paired with positive expressions were assessed. In particular, the role of contingency between toys' movements and an actress's emotional expressions as well as the role of gaze direction toward the toys' location were examined. Infants were habituated to alternating films of two toys each paired with an actress's affective expression (happy and fearful) under contingent or noncontingent and gaze congruent or gaze incongruent conditions. Results indicated that gaze congruence and contingency between toys' movements and a person's affective expressions were important for infant perception of affect-object relations. Furthermore, infant perception of the relation between affective expressions and toys translated to their manual preferences for the 3-dimensional toys. Infants who received contingent affective responses to the movements of the toys spent more time touching the toy that was previously paired with the positive expression. These findings demonstrate the role of contingency and gaze direction in the emergence of social referencing in the first half year of life.^

Structure-based modeling of head -related transfer functions towards interactive customization of binaural sound systems

One of the most popular techniques for creating spatialized virtual sounds is based on the use of Head-Related Transfer Functions (HRTFs). HRTFs are signal processing models that represent the modifications undergone by the acoustic signal as it travels from a sound source to each of the listener's eardrums. These modifications are due to the interaction of the acoustic waves with the listener's torso, shoulders, head and pinnae, or outer ears. As such, HRTFs are somewhat different for each listener. For a listener to perceive synthesized 3-D sound cues correctly, the synthesized cues must be similar to the listener's own HRTFs. ^ One can measure individual HRTFs using specialized recording systems, however, these systems are prohibitively expensive and restrict the portability of the 3-D sound system. HRTF-based systems also face several computational challenges. This dissertation presents an alternative method for the synthesis of binaural spatialized sounds. The sound entering the pinna undergoes several reflective, diffractive and resonant phenomena, which determine the HRTF. Using signal processing tools, such as Prony's signal modeling method, an appropriate set of time delays and a resonant frequency were used to approximate the measured Head-Related Impulse Responses (HRIRs). Statistical analysis was used to find out empirical equations describing how the reflections and resonances are determined by the shape and size of the pinna features obtained from 3D images of 15 experimental subjects modeled in the project. These equations were used to yield “Model HRTFs” that can create elevation effects. ^ Listening tests conducted on 10 subjects show that these model HRTFs are 5% more effective than generic HRTFs when it comes to localizing sounds in the frontal plane. The number of reversals (perception of sound source above the horizontal plane when actually it is below the plane and vice versa) was also reduced by 5.7%, showing the perceptual effectiveness of this approach. The model is simple, yet versatile because it relies on easy to measure parameters to create an individualized HRTF. This low-order parameterized model also reduces the computational and storage demands, while maintaining a sufficient number of perceptually relevant spectral cues. ^