_After-images._ Images that follow immediately after stimulation of a sense organ, and resulting from this stimulation.
_Association._ Binding together ideas through experiencing them together.
_Attention._ Relative clearness of perceptions and ideas.
_Attitude._ The tendency toward a particular type of response in action or a particular idea or association in thought.
_Bond._ The connection established in the nervous system which makes a certain response follow a certain stimulus or a certain idea follow another idea or perception.
_Capacity._ The possibility of learning, achieving, etc.
_Color blindness._ Inability to experience certain colors, usually red and green.
_Complementary color._ Complementary colors are those which, mixed in the right proportion, produce gray.
_Connection._ The nerve-path through which a stimulus produces a response or through which one idea produces or evokes another.
_Conscious._ Having consciousness, or accompanying consciousness or producing consciousness.
_Consciousness._ The mental states--perceptions, ideas, feelings--which one has at any moment.
_Low level of consciousness._ Conscious processes not so clear as others existing at the same time.
_High level of consciousness._ Conscious processes that are clear as compared to others existing at the same time.
_Contrast._ The enhancing or strengthening of a sensation by another of opposite quality.
_Correlation._ The relation that exists between two functions, characteristics, or attributes that enables us, finding one, to predict the presence of the other.
_Development._ The appearance, or growth, or strengthening of a characteristic.
_Emotion._ The pleasure-pain aspect of experience plus sensations from characteristic bodily reactions.
_Environment._ The objects and forces about us which affect us through our senses.
_Environmental instincts._ Instincts which have originated, at least in part, from the periodic changes in man's environment.
_Eugenics._ The science of race improvement through selective breeding or proper marriages or in some cases through the prevention of marriage.
_Experience._ What we learn of the world through sensation and perception.
_Fatigue._ Inability to work produced by work and which only rest will cure.