It is interesting to note that, if provided with specific exemplars, moderately impaired subjects are able sort them into very broad categories. As the disease progresses DAT patients have been shown to focus more on concrete rather than abstract (kind, order) categories. Concrete categories are of course less general or universal and therefore more idiosyncratic which is to say derived from personal experience. Individual differences become paramount as concrete categories and specific memories become the sole understanding that DAT sufferers retain. The progression of Alzheimer Disease has been compared to a process of reverse maturation and sufferers in advanced stages are often likened to four-year olds. However, these analogies may fail to appreciate the frustration and anger that result from DAT sufferers awareness of their own limitations and the nonreversible qualities of identity and emotional depth. Caregivers identify the emotional impact of the disease as among the most severe, describing communication between patient and caregiver as severely strained. Such strains make it hard for the caregiver to initiate, as a solo act, confident interactions that are emotionally positive. As a result, the severity of the patient's loss becomes something routine and the sufferer is no longer greeted or treated as the person he or she was prior to illness. This is unfortunate considering the fact that feelings of comfort, security, happiness, and sexuality do remain in tact in advanced stages of Alzheimer disease. Nowhere is this fact more evident than in the general appeal of music, humming, and sentiments conveyed through voice to sufferers of DAT. Just as skills or procedural memories remain in tact as a kind of unconscious or at least computationally non-intensive memory, the automaticity of auditory recognition and visual perception also survive even in advances stages of the disease.