Interest - Excitement
Any increase in brain activity by any stimulus will trigger the affect of Interest-Excitement. The stimulus may be obvious such as a sound, something visual or a smell but it may also be impossible to discern externally such as a recalled image, a memory or the need for food or drink.
The brow will furrow, the gaze becomes intent, rapt inattention, listening and the eyes tracking. The stimulus may be regularly repeated events, or by a need to be satisfied such as hunger or thirst. Tomkins argues that interest-excitement is always stimulated by an increase in the density of neural firing- i.e. the rate at which is nervous system send signals to the brain.
Enjoyment - Joy
Enjoyment-Joy is always produced by a reduction in brain activity, in the rate of neural firing. Such reduction in brain activity will produce a smile with the lips widened up and out. A level of calm and contentment will ensue. Any stimulus that produces a reduction in high-level activity will produce a smiling face.
Surprise - Startle
The facial expression is eyebrows up, eyes wide open, blink and mouth open. There is often a rapid intake of breath followed by expiration when the lips may be protruded, including a vocal exclamation such as "Oh" or even a profanity! Tomkins originally considered it to be a positive affect but it is now generally accepted as neutral (Nathanson 1992). Depending on earlier experiences and memories it may be personally perceived as a positive or negative affect, evoking a positive or negative response.