Affect vs. emotion

Chapter 4 endnote 36, from How Emotions are Made: The Secret Life of the Brain by Lisa Feldman Barrett.
Some context is:

Scholars and scientists have confused affect and emotion for centuries.

Affect is your basic sense of feeling, ranging from unpleasant to pleasant (called valence), and from idle to activated (called arousal). Emotion is a much more complex mental construction.

Many scientists use the word “affect” when really they mean emotion. They’re trying to talk about emotion cautiously, in a non-partisan way, without taking sides in any debate. As a result, in the science of emotion, the word "affect" can sometimes mean anything emotional. This is unfortunate, because affect is not specific to emotion; it is a feature of consciousness. Affect occurs in every moment (whether you're aware of it or not) because interoception occurs in every moment.

Conversely, sometimes scientists use the word “emotion” when really they mean affect. For example, scientists who study how people remember pleasant and unpleasant events sometimes describe what they study as “emotional memory,” but "pleasant" vs. "unpleasant" is a distinction of affect; the findings really reveal how people remember instances of intense valence and arousal (i.e., affect).

This confusion between affect and emotion has resulted in numerous scientific errors. For example, many scientists believed that young infants can discriminate facial configurations for different emotions like happiness, anger, fear, and sadness. The overwhelming majority of experiments on this topic, however, compare only whether infants can distinguish positive from negative, or high arousal from neutral, in stereotyped facial poses. For example, they will test whether infants can distinguish between posed faces:

• Scowling (angry) vs. smiling (happy) faces, which is distinguishing valence
• Wide-eyed, startled (fearful) vs. neutral faces, which is again distinguishing valence
• Scowling (angry) vs. pouting (sad) faces, which is distinguishing arousal

The same is true for studies emotion in non-human primates. These are all tests of affect, not emotion.