Different Kinds of Intelligence

from a letter to me by Grady Towers dated March 23, 1999
Used with permission from the author

You are no doubt aware that psychometricians acknowledge two different kinds of intelligence: fluid and crystallized. What may surprise you to learn is that this is a very old formulation, and the most modern factor analytic studies, by the very best factor analysts, recognize nine different kinds of general mental ability (See Intellectual Development, edited by Robert J. Sternberg and Cynthia A. Berg, chapter 3). Here's what they are:

Fluid reasoning (Gf), measured in tasks requiring inductive, deductive, conjunctive, and disjunctive reasoning to arrive at understanding relations among stimuli, comprehend implications, and draw inferences.

Acculturation Knowledge (Gc), measured in tasks indicating breadth and depth of the knowledge of the dominant culture.

Quantitative Knowledge (Gq), measured in tasks requiring understanding and application of the concepts and skills of mathematics.

Short-term apprehension-retrieval (Gsm), also called short-term memory, measured in a variety of tasks that mainly require one to maintain awareness of, and be able to recall, elements of immediate stimulation -- i.e., events of the last minute or so.

Fluency of retrieval from long-term storage (Glr), also called long-term memory, measured in tasks that indicate consolidation for storage and mainly require retrieval, through association, of information stored minutes, hours, weeks, and years before.

Visual processing (Gv), measured in tasks involving visual closure and constancy, and fluency in "image-ing" the way objects appear in space as they are rotated and flip-flopped in various ways.

Auditory processing (Ga), measured in tasks that involve perception of sound patterns under distraction or distortion, maintaining awareness of order and rhythm among sounds, and comprehending elements of groups of sounds, such as chords and the relations among such groups.

Processing speed (Gs), although involved in almost all intellectual tasks (Hertzog, 1989), measured most purely in rapid scanning and responding in intellectually simple tasks (in which almost all people would get the right answer if the task were not highly speeded).

Correct decision speed (CDS), measured in quickness in providing answers in tasks that require one to think.


My own factor analytic studies of the super-high IQ community have never been as complete as I could have wanted. Sample sizes were too small, and the variety of items was too restricted. Nevertheless, I have some informed opinions. My guess is that ThinkFast is a test of CDS. I believe the LAIT to be a nearly pure measure of fluid g (Gf), the verbal portion of the Mega Test to be mostly a measure of acculturation knowledge (Gc), and the non-verbal subsection to be a mixture of fluid intelligence (Gf) and quantitative knowledge (Gq). But the Mobius Test, which was making the rounds a few years ago, is the most interesting of all. My best guess is that it is mostly a test of fluency of retrieval from long term storage (Glr), the first time I've ever seen this factor on a test in such a pure form.

Each of these mental abilities peak at different ages. The average scores for Gf, Gsm, Gs, and CDS decrease steadily from the early twenties onward. The averages for Gv and Ga increase into the late thirties and early forties then begin to decline. The averages for Gc, Glr, and Gq increase into the sixties before showing a decline.

In other words, whichever kind of intelligence a high IQ society favors will influence the average age of its membership. Perhaps a mixture would be wise.

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