cues are equal. This is defined as phonetic trading relation (Luce & Pisoni, 1986). In natural speech almost every phonetic contrast is cued by numerous distinct acoustic properties of the speech signal. According to Moore (1997), a change in the setting or value of one cue, which leads to a change in the phonetic perception, can be offset by an opposed setting of a change in another cue so as to maintain the original phonetic perception. This is referred to as cue trading or phonetic trading. Cue trading generally occurs in speech stimuli, however one should not assume that trading relations never occur for non-speech stimuli. Evidence has shown that trading relations can be found for stimuli that have some speech like properties but are not actually perceived as speech. The reality that trading relations differ depending on whether stimuli are perceived as speech or non-speech, provides great support for the concept of a speech mode of perception (Moore, 1997).Audiovisual IntegrationSpeech perception is not solely dependent upon what we hear. Other factors such as sight play a major role in perception. For example, when observers are presented acoustically with /ba/, but see a face saying /de/, they will often perceive the sound as /da/. This sound is derived from combining the consonant that they saw and the vowel that they heard. This result is typically experienced as slightly imperfect by comparison with the normal case in which acoustical and optical stimuli are in agreement. The observers cannot tell what the nature of the imperfection is. They are not able to say that it is because they heard one thing and saw something else being said. The conclusion is the McGurk effect. It provides strong evidence for the equivalence in phonetic perception of two different kinds of physical information. Since the acoustic and optical stimuli are providing information about the same phonetic gesture, and it is the gesture that ...
