ensations 197

The Skin Senses 197

The Sense of Taste 201

The Sense of Smell 203

Organic Sensations 204

The Sense of Sight 204

Simpler Forms of the Color Sense 209

Visual Sensations as
Related to the Stimulus 212

Color Mixing 214

What Are the Elementary
Visual Sensations? 216

Theories of Color Vision 220

Adaptation 224

Rod and Cone Vision 226

After-images 226

Contrast 227

The Sense of Hearing 228

Comparison of Sight and Hearing 231

Theory of Hearing 234

Senses of Bodily Movement 236

Exercises 241

References 243

CHAPTER XI

ATTENTION 244

The Stimulus, or
What Attracts Attention 245

The Motor Reaction in Attention 248

The Shifting of Attention 251

Laws of Attention and
Laws of Reaction in General 256

Sustained Attention 257

Distraction 259

Doing Two Things at Once 260

The Span of Attention 261

Summary of the Laws of Attention 262

Attention and Degree of Consciousness 265

The Management of Attention 267

Theory of Attention 268

Exercises 270

References 270

CHAPTER XII

INTELLIGENCE 271

Intelligence Tests 272

Performance Tests 275

Group Testing 276

Some Results of the Intelligence Tests 278

Limitations of the Intelligence Tests 281

The Correlation of Abilities 288

General Factors in Intelligence 285

Special Aptitudes 288

Heredity of Intelligence
and of Special Aptitudes 289

Intelligence and the Brain 292

Exercises 294

References 295

CHAPTER XIII

LEARNING AND HABIT FORMATION 296

Acquired Reactions Are
Modified Native Reacti