The flow of information within modern information society has increased
rapidly over the last decade. The major part of this information flow
relies on the individual’s abilities to handle text or speech input. For
the majority of us it presents no problems, but there are some
individuals who would benefit from other means of conveying information,
e.g. signed information flow. During the last decades the new results
from various disciplines have all suggested towards the common
background and processing for sign and speech and this was one of the
key issues that I wanted to investigate further in this thesis. The
basis of this thesis is firmly within speech research and that is why I
wanted to design analogous test batteries for widely used speech
perception tests for signers – to find out whether the results for
signers would be the same as in speakers’ perception tests. One of the
key findings within biology – and more precisely its effects on speech
and communication research – is the mirror neuron system. That finding
has enabled us to form new theories about evolution of communication,
and it all seems to converge on the hypothesis that all communication
has a common core within humans.



In this thesis speech and sign are discussed as equal and analogical
counterparts of communication and all research methods used in speech
are modified for sign. Both speech and sign are thus investigated using
similar test batteries. Furthermore, both production and perception of
speech and sign are studied separately. An additional framework for
studying production is given by gesture research using cry sounds.
Results of cry sound research are then compared to results from children
acquiring sign language. These results show that individuality
manifests itself from very early on in human development. Articulation
in adults, both in speech and sign, is studied from two perspectives:
normal production and re-learning production when the apparatus has been
changed. Normal production is studied both in speech and sign and the
effects of changed articulation are studied with regards to speech. Both
these studies are done by using carrier sentences. Furthermore, sign
production is studied giving the informants possibility for spontaneous
speech. The production data from the signing informants is also used as
the basis for input in the sign synthesis stimuli used in sign
perception test battery.



Speech and sign perception were studied using the informants’
answers to questions using forced choice in identification and
discrimination tasks. These answers were then compared across language
modalities. Three different informant groups participated in the sign
perception tests: native signers, sign language interpreters and Finnish
adults with no knowledge of any signed language. This gave a chance to
investigate which of the characteristics found in the results were due
to the language per se and which were due to the changes in modality
itself.



As the analogous test batteries yielded similar results over
different informant groups, some common threads of results could be
observed. Starting from very early on in acquiring speech and sign the
results were highly individual. However, the results were the same
within one individual when the same test was repeated. This
individuality of results represented along same patterns across
different language modalities and - in some occasions - across language
groups. As both modalities yield similar answers to analogous study
questions, this has lead us to providing methods for basic input for
sign language applications, i.e. signing avatars. This has also given us
answers to questions on precision of the animation and intelligibility
for the users – what are the parameters that govern intelligibility of
synthesised speech or sign and how precise must the animation or
synthetic speech be in order for it to be intelligible. The results also
give additional support to the well-known fact that intelligibility in
fact is not the same as naturalness. In some cases, as shown within the
sign perception test battery design, naturalness decreases
intelligibility. This also has to be taken into consideration when
designing applications.



All in all, results from each of the test batteries, be they for
signers or speakers, yield strikingly similar patterns, which would
indicate yet further support for the common core for all human
communication. Thus, we can modify and deepen the phonetic framework
models for human communication based on the knowledge obtained from the
results of the test batteries within this thesis.