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Processing speed and the Block Design subtest on WAIS
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Horus
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PostPosted: Fri Aug 27, 2010 7:18 pm    Post subject: Processing speed and the Block Design subtest on WAIS Reply with quote

My scores on the Block Design subtest on WAIS have always been roughly the same. I always score either a 6 or 7 on block design, which is in the low average range. Aside from Object Assembly and the Visual Puzzles subtests, block design has always been my lowest score out of all subtests on all versions of WAIS. Object Assembly is no longer used on the latest version of WAIS (IV) and I suppose that is because the OA subtest had the lowest reliability coefficient (.68 I believe) out of all the WAIS subtests. The Visual Puzzles subtest is now included on the latest version of WAIS and it is considered more reliable than Object Assembly. I suppose that is due (at least in part) to the fact that the Visual Puzzles subtest does not involve motor skills.


Considering processing speed (especially visual processing it would seem) has always been a weakness for me, I am assuming my poor performance on block design has something to do with my scores on that subtest since it is timed. This is not to say I believe my visual-constructional skills would be good even if I had no problems with processing speed, but I think my performance on this subtest would be somewhat better if processing speed wasn't an issue. I'll use the most recent block design subtest I took as an example.


I arranged most of the block patterns correctly within the alloted time frame. It did take me nearly all the alloted time to do so on quite a few of the patterns however. I only failed to arrange the blocks correctly within the alloted time frame on the very last pattern displayed in the WAIS booklet. I received a six on this particular block design subtest, which is in the low average range. My processing speed index score on this WAIS was 86, which is just on the cusp of borderline.

The thing that seems somewhat odd to me is that I scored a seven on one block design subtest and my processing speed index score on that WAIS was 108. That is over one standard deviation higher than my processing speed index score on this latest WAIS. Now i'm pretty sure my processing speed still could've been a factor on that block design subtest in spite of my higher processing speed index score. For one thing....I believe the index score is an estimate of one's processing speed overall and therefore may not indicate much in and of itself regarding any deficits in VISUAL processing. I'm just wondering how speed is taken into account on the block design subtest.


For example.....say two people assemble all, or at least most, of the block patterns correctly within the alloted time frame. If one does so within a minute and the other arranges them correctly within 25 seconds, i'm almost certain the first person would receive the lower score. Am I correct here or is there something i'm missing in terms of how they calculate the results of the block design subtest? Furthermore, how can they determine that someone has a fundamental problem with visual-constructional skills/reasoning when the cause of the problem may have everything to do with a deficit in processing speed? It seems like they're largely basing all this on processing speed and that doesn't strike me as very fair. Should person X be viewed as someone with greater difficulties in visual-constructional skills than person Y simply because it takes person X longer to correctly complete the tasks that supposedly measure these skills?

In a practical real-world sense....speed certainly does matter when it comes to these things. But how can clinicians differentiate between actual problems with visual-constructional REASONING and mere deficits in visual processing speed? It seems to me that they don't make this distinction very well. My neuropsychologist wasn't very clear as to whether my low performance on block design was simply reflective of deficits in visual processing speed or if I have significant deficits in visual-constructional reasoning itself.
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pgd
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PostPosted: Fri Aug 27, 2010 8:00 pm    Post subject: Re: Processing speed and the Block Design subtest on WAIS Reply with quote

My personal view is that a lot of these tests are good but imperfect.

Some of these tests give false results when given only one time to those who have subtle neurological challenges such as:

ADHD Inattentive
Central auditory processing disorder
Petit mal/absence/complex partial/TLE and so on
Imperfect peripheral vision
Nystagmus
Strabismus
Constructional apraxia
Mild dyspraxia
Sports concussions/subtle brain injuries
Subtle cerebral palsy

and so on.

Sometimes there can be a noticeable difference in scores when these tests are given:

in a med-free state

or

when using an effective medicine for a neurological challenge such as epilepsy or ADHD.

Generally speaking, these tests should be given (for those with the above kinds of challenges) at least twice or more over a period of several years, however, many health care plans will not do this.

Many health care plans today will not test for autism, Asperger, ADHD, central auditory processing disorder, or dyspraxia at all.

Many of these tests are designed as mass production tests and given to the masses as such.

These tests simply fail to give the best answers to those with subtle neurological challenges unless they are given more than once under varying conditions.

That's my understanding.
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anbuend
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PostPosted: Fri Aug 27, 2010 9:27 pm    Post subject: Reply with quote

I think Processing Speed isn't an actual literal description of how fast you process information, but rather a score derived by calculating a number based on two or different subtests. Just because it's called "processing speed" doesn't mean that it reflects some kind of absolute determination of processing speed.

Which makes sense because there are many different forms and kinds of processing speed. I process many things quite slowly, and yet my score on Block Design was my highest subscale score. Because it dealt with an area that I happen to be good at. I'm quite good at dealing with patterns of shapes, which is what it tests. If someone were to test the way I process categories (I don't know the best word for it, but like identifying "table" and "dog" and things like that), it would be a much slower processing speed than the way I process something closer to the raw stimuli without having to evaluate them to determine "what" they are.

Someone recently posted something about how "processing speed" is really a combination of a zillion different skills, and depends on which part of your brain is doing the processing, what it's processing for, what information is being processed, and what the person is going to do with it. It's not a singular thing, and the Processing Speed part of the IQ test should really just be called "Digit Symbol Coding + Symbol Search" because that's all it is.

My test didn't have Symbol Search that I'm aware of. But Digit Symbol Coding was my worst score on the entire test, well into the lowest range of possible subscores (don't remember it exactly). Which means that it's quite likely that my Processing Speed score, if calculated, would be in the MR range. And yet my Block Design score is either above average or high average, can't remember which.

All of which is to say, the reason your Processing Speed score and your Block Design score aren't the same is because they measure entirely different things. Processing Speed is determined by your performance in Digit Symbol Coding and in Symbol Search. Block Design is determined by, well, Block Design. Digit Symbol Coding and Symbol Search don't measure the same thing that Block Design measures. Which is why you have high Processing Speed and low Block Design and I have the opposite. Totally different subtests.
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