A specific category in human cognition, size representation, was disrupted by the application of cortical electrical interference through a recently modified technique involving implantation of indwelling subdural electrode arrays. When subjected to electrical stimulation at a specific site, the subject was unable to access size information when questioned verbally, but showed no deficit if the size discrimination was presented visually. Verbal questions about size were answered correctly when the patient was not subjected to cortical interference. Other measures of verbal and visual comprehension for the categories of color, shape, orientation, movement, texture, and structure, tested under cortical interference, were normal. This clear-cut distinction between verbal and visual access to information about size, shown by a reversible block at a known and anatomically circumscribed site, provides further evidence that higher order neural processing is categorically represented.