Tonic immobility vs Freezing - Not the same!

 

Figure 1. Schematic of routes of defensive behaviour (adapted from Hagenaars et al. [15]). (Online version in colour.)

Measurement 

The Tonic Immobility subscale of the Tonic Immobility Scale (TIS-TI) (Fusé et al., 2007) was used to measure immobility reactions during trauma. The TIS-TI subscale contains 7 self-report items which are scored on a 7-point Likert scale, ranging from 0 (not at all) to 6 (extremely/very much). Total scores range from 0 to 42. An example item is “Rate the degree to which you were unable to move even though not restrained”. Internal consistency was acceptable to strong for TIS-TI in larger samples (Cronbach's α = 0.71 to 0.94) (Fusé et al., 2007; Hagenaars, 2016; De Kleine et al., 2018). Following Hagenaars (2016) we used two items of the TIS subscale for Fear to assess peritraumatic fear (TIS-Fear). An example item is “Rate the extent to which you felt feelings of fear/panic during the event”. The original Fear subscale consisted of 3 items. However, one item of this subscale assesses peritraumatic dissociation and did not load on the fear factor in several studies (Abrams et al., 2009; Hagenaars, 2016). Following Hagenaars (2016), this item was used to assess peritraumatic dissociation (TIS-Diss; “Rate the extent to which you felt detached from what was going on around you during the event”). Total scores range from 0 to 12 for TIS-Fear and 0 to 6 for TIS-Diss.