Attractor

A particular solution of a dynamical system to which other solutions converge in time.  Attractors can be constant in time, periodic, or have more complex time dependencies (e.g., chaos).  They are (asymptotically) stable in the sense that the dynamical system evolves such as to approach the attractor in whose vicinity the system starts out.  If …

Attributable fraction

The proportion of cases of some negative outcome (e.g., emphysema)) that may be attributable to a particular risk (e.g., smoking tobacco). See Epidemiology, Emphysema, Environmental tobacco smoke (ETS), Hazard ratio, Indices of efficacy, Odds ratio, Risk factors

Attractions

Positive forces that bring persons together, including combinations of behavior and physical features.  One such force, at least in adults, is the support offered by another person when one encounters difficulties.  Others identified include proximity (geographically including something as seemingly mundane as seating in a classroom), association (e.g., sharing the same opinions), similarity (e.g., in …

Attentional flexibility

The capacity to shift the focus of attention from one task to another.  This involves the ability to initiate, focus, sustain, inhibit and transfer attention.  This capacity is typically measured by performance on card sorting tasks, in which the sorting rule is periodically changed; impaired performance on such tasks can involve difficulties in disengaging from …

Attention deficit hyperactivity disorder (ADHD)

A relatively common and diffuse childhood disorder, it is a constellation of problems that become manifest in children entering school, characterised by inattentiveness, hyperactivity, poor impulse control, behaviour management problems, and a high risk of other co-morbid behaviours and academic problems.  First described by Heinrich Hoffmann (1809-1894) in 1845, it was not until 1902, following …

Attention

There are a number of meanings associated with the term such as visual attention, auditory attention, top-down and bottom-up controlled attention, and so on.  In general, it refers to the selective and sustained aspects of perception that focus on certain features of the environment to the relative exclusion of other features.  It may be conscious …

Attachment

A positive social relationship between a child and a parent that fosters feelings of security in the presence of the parent and distress in the parent’s absence.  If attachment is secure, as revealed by the strange situation test, then the child can readily separate from the primary caregiver, and actively seeks that person out on …

Attachment theory

Usually refers to the theory proposed by John Bowlby (1907-1990) and developed further by Mary D. Salter Ainsworth (1913-1999) that is meant to explain how an infant develops emotional relationships with the mother or another caregiver, and how they relate to subsequent development.  Attachment behaviors, forming a system, are assumed to be biological predispositions that …

Ataxia

Sometimes referred to as dyssynergia, it is a diminution or loss of coordination over voluntary movements and balance that can result, for example, in a staggering gait.  Classified as a type of cerebral palsy, it is due to degeneration of the cerebellum or lesions in other areas of the central nervous system (e.g., in the …