Cervical dystonia is the most frequent phenotype of adult-onset idiopathic isolated focal dystonia; its pathogenesis is unknown. A marker that is more penetrant, an endophenotype, may reveal disease pathomechanisms. Abnormal temporal discrimination threshold is an endophenotype for cervical dystonia. We hypothesise that both abnormal temporal discrimination and cervical dystonia are due to disordered covert attentional orienting involving the superior colliculi (SC). Looming stimuli indicate potential threat and activate the SC. The aim of this study was to assess, by functional magnetic resonance imaging (fMRI), the response of the SC to a looming stimulus in cervical dystonia patients and their unaffected relatives with and without abnormal temporal discrimination. We examined by fMRI the responses to looming, receding and random stimuli at whole brain and superior collicular level in 32 participants with abnormal temporal discrimination and 32 participants with normal temporal discrimination. Compared to the 32 participants with normal temporal discrimination, the 32 participants with abnormal temporal discrimination demonstrated (i) disrupted superior collicular activation to looming stimuli; (ii) significantly reduced superior collicular activation for whole brain and region of interest analysis to looming stimuli; (iii) a statistically significant negative correlation between TDT z-score and superior collicular peak values during the loom condition. Our results suggest that an abnormal temporal discrimination threshold is associated with disrupted superior collicular processing. The findings from our study shed new light on potential pathomechanisms in cervical dystonia.