A tic is a sudden and repetitive motor movement or vocalization that is not rhythmic and involves discrete muscle groups.[1][2][3] It is typically brief and may resemble a normal behavioral characteristic or gesture.[4]
Tics can be invisible to the observer, such as abdominal tensing or toe crunching. Common motor and phonic tics are, respectively, eye blinking and throat clearing.[5]
^Leckman JF, Bloch MH, King RA, Scahill L (2006). "Phenomenology of tics and natural history of tic disorders". Adv Neurol. 99: 1–16. PMID16536348.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^Nind M, Kellett M (2002). "Responding to individuals with severe learning difficulties and stereotyped behaviour: challenges for an inclusive era". Eur J Spec Needs Educ. 17 (3): 265–82. doi:10.1080/08856250210162167. S2CID142836660.