Page 110 - Designing Sociable Robots

breazeal-79017 book March 18, 2002 14:54

The Auditory System 91

350
approval
attention
soothing
neutral
300
prohibition
250

Energy Variance 200

150

100

50

0
100 150 200 250 300 350 400 450 500 550
Pitch Mean
Figure 7.4
Feature space of all five classes with respect to energy variance, F 9 , and pitch mean, F 1 . There are three distin-
guishable clusters for prohibition, soothing and neutral, and approval and attention.

samples are clustered in the low pitch mean and low energy variance region. The neutral
samples have low pitch mean and are divided into two regions in terms of their energy
variance values. The neutral samples with high energy variance are clustered separately
from the rest of the classes (in between prohibition and soothing), while the ones with
lower energy variance are clustered within the soothing class. These findings are consistent
with the proposed prior knowledge. Approval, attention, and prohibition are associated with
high intensity while soothing exhibits much lower intensity. Neutral samples span from low
to medium intensity, which makes sense because the neutral class includes a wide variety
of utterances.
Based on this observation, the first classification stage uses energy-related features to
classify soothing and low-intensity neutral with from the other higher intensity classes (see
figure 7.5). In the second stage, if the utterance had a low intensity level, another classifier

decides whether it is soothing or neutral. If the utterance exhibited high intensity, the F 1 -F 9
pair is used to classify among prohibition, the approval-attention cluster, and high intensity