behaviours discrepant with the A, B and C classifications, a fourth classification was added by Ainsworth's colleague Mary Main. In the Strange Situation, the attachment system is expected to be activated by the departure and return of the caregiver. If the behaviour of the infant does not appear to the observer to be coordinated in a smooth way across episodes to achieve either proximity or some relative proximity with the caregiver, then it is considered 'disorganized' as it indicates a disruption or flooding of the attachment system (e.g. by fear). Infant behaviours in the Strange Situation Protocol coded as disorganized/disoriented include overt displays of fear; contradictory behaviours or affects occurring simultaneously or sequentially; stereotypic, asymmetric, misdirected or jerky movements; or freezing and apparent dissociation. Lyons-Ruth has urged, however, that it should be more widely "recognized that 52% of disorganized infants continue to approach the caregiver, seek comfort, and cease their distress without clear ambivalent or avoidant behavior". The benefit of this category was hinted at earlier in Ainsworth's own experience finding difficulties in fitting all infant behaviour into the three classifications used in her Baltimore study. Ainsworth and colleagues sometimes observed "tense movements such as hunching the shoulders, putting the hands behind the neck and tensely cocking the head, and so on. It was our clear impression that such tension movements signified stress, both because they tended to occur chiefly in the separation episodes and because they tended to be prodromal to crying. Indeed, our hypothesis is that they occur when a child is attempting to control crying, for they tend to vanish if and when crying breaks through." Such observations also appeared in the doctoral theses of Ainsworth's students. Crittenden, for example, noted that one abused infant in her doctoral sample was classed as secure (B) by her undergraduate coders because her strange situation behaviour was "without either avoidance or ambivalence, she did show stress-related stereotypic headcocking throughout the strange situation. This pervasive behavior, however, was the only clue to the extent of her stress". There is rapidly growing interest in disorganized attachment from clinicians and policy-makers as well as researchers. However, the disorganized/disoriented attachment (D) classification has been criticized by some for being too encompassing, including Ainsworth herself. In 1990, Ainsworth put in print her blessing for the new 'D' classification, though she urged that the addition be regarded as "open-ended, in the sense that subcategories may be