intertwined that the two are combined in a single phonological system, where neither can be considered without the other. The distinctions of such systems are termed registers. The tone register here should not be confused with register tone described in the next section. Phonation type Gordon and Ladefoged established a continuum of phonation, where several types can be identified. Relationship with tone Kuang identified two types of phonation: pitch-dependent and pitch-independent. Contrast of tones has long been thought of as differences in pitch height. However, several studies pointed out that tone is actually multidimensional. Contour, duration, and phonation may all contribute to the differentiation of tones. Recent investigations using perceptual experiments seem to suggest phonation counts as a perceptual cue. Tone and pitch accent Many languages use tone in a more limited way. In Japanese, fewer than half of the words have a drop in pitch; words contrast according to which syllable this drop follows. Such minimal systems are sometimes called pitch accent since they are reminiscent of stress accent languages, which typically allow one principal stressed syllable per word. However, there is debate over the definition of pitch accent and whether a coherent definition is even possible. Tone and intonation Both lexical or grammatical tone and prosodic intonation are cued by changes in pitch, as well as sometimes by changes in phonation. Lexical tone coexists with intonation, with the lexical changes of pitch like waves superimposed on larger swells. For example, Luksaneeyanawin (1993) describes three intonational patterns in Thai: falling (with semantics of "finality, closedness, and definiteness"), rising ("non-finality, openness and non-definiteness") and "convoluted" (contrariness, conflict and emphasis). The phonetic realization of these intonational patterns superimposed on the five lexical tones of Thai (in citation form) are as follows: With convoluted intonation, it appears that high and falling tone conflate, while the low tone with convoluted intonation has the same contour as rising tone with rising intonation. Tonal polarity Languages with simple tone systems or pitch accent may have one or two syllables specified for tone, with the rest of the word taking a default tone. Such languages differ in which tone is marked and which is the default. In Navajo, for example, syllables have a low tone by default, whereas marked syllables have high tone. In the related language Sekani, however, the default is high tone, and marked syllables have low tone. There are parallels with stress: English