4.2 B. External CHC structural extensions
“For any taxonomic model of human cognitive abilities to be complete, all sensory moralities must be encompassed within its framework (Carroll, 1993; Roberts et al., 1999; Stankov, Seizova- Cajic, & Roberts, 2001)” (Danthiir, Roberts, Pallier & Stankov, 2001).   Currently, a significant gap exits in the CHC taxonomy regarding the human sensory domains of tactile, kinesthetic, and olfactory abilities (Danthiir et al., 2001).  Recent factor analytic research argues for the expansion of the CHC taxonomy to include a number of additional broad ability constructs. 
Tactile (Gh) and kinesthetic (Gk) abilities
Despite the historical and frequent use of measures of tactile and kinesthetic abilities in neuropsychological assessment settings (e.g., Dean-Woodcock Neuropsychological Battery, Dean & Woodcock, 2003; Halstead- Reitan Neuropsychological Test Battery, Reitan & Wolfson, 1985;  Luria-Nebraska Neuropsychological Test Batteries, Golden, Hammeke & Purisch, 1985), and the importance of understanding how these processes are used by individuals with visual impairments to navigate in the absence of  on non-visual cues (Klatzky, Golledge, Loornis, Cicinelli, & Pellegrino, 1995), the structural evidence for these domains has been meager (Carroll, 1993).  Since Carroll’s factor analytic meta-analysis, a handful of new studies (Li, Jordanova & Lindenberger 1998; Pallier, Roberts, & Stankov, 2000; Roberts, Stankov, Pallier & Dolph, 1997; Stankov, Senzova-Cajic & Roberts, 2001) have factored sets of tactile and kinesthetic variables together with cognitive variables.  Collectively, these studies have tentatively suggested that separate broad kinesthetic (Gk) and tactile (Gh) abilities should be included in a more comprehensive CHC taxonomy (Stankov, 2000). [Note. Gk = kinesthetic; Gh = tactile (“h” stands for “haptic”) as per the Stankov research group notation.   ]
The Stankov group isolated three different abilities at the narrow (stratum I) ability level.  The TP (Tactile Performance) factor reflected the ability to perform complex tactile-kinesthetic tasks. The complexity of the TP ability was due to the inability of these researchers to “disentangle” TP from the higher- order influences of Gv and Gf.  In terms of practical test interpretation issues, Stankov (2000) concluded that the interpretation of the complex Halstead- Reitan tactile and kinesthetic tasks may be problematic as it was not possible to isolate separate tactile and kinesthetic factors distinct from Gv. “In other words, the processes involved in complex tactile and kinesthetic tasks seem to activate visualization abilities during their performance, a finding in agreement with the experimental literature (e. g., Livesey & Intili, 1996)” (Stankov, 2000, p. 42). 
The Stankov group also identified separate Tactile (TS) and Kinesthetic (KS) abilities.  TS abilities “require processing that depends on fine discrimination of pressure on the skin” while KS abilities involve “the awareness of (passive) movements of upper limbs and the ability to visually recognize path that individuals follow while blindfolded” (Stankov, 2000, p. 43).   The kinesthetic (KS) and tactile (TS) factors were found to be weakly correlated with higher- stratum cognitive abilities (e.g., Gv, Ga, Gf, etc.; Stankov et al, 2001).  The common variance among the cognitively simple KS and TS factors “cast doubt on the existence of a broad ability that spans the kinesthetic and tactile domains” (Stankov et al., 2001, p.25).
In a sample of 179 middle age adults, Li, Jordanova and Lindenberger (1998) isolated two tactile discrimination abilities (i.e., Tactile Pressure Sensitivity and Texture Discrimination) and one tactile similarity (Arc-Part part whole matching) ability.   All three factors bear resemblance to the TS ability described by the Stankov group.  Given that each of Li et al.’s (1998)  three factors were based on multiple scores from each of the three different tasks, it is possible that these three factors may represent singlet test factors and not separate abilities.  Until replicated, the differentiation of TS into sub-abilities is not encouraged. [Note. It is important to note than Li et al (1998) included their tactile factors, together with visual and auditory acuity factors, as causal variables with direct effects on g, which in turn was represented by a measurement model consisting of five latent factor cognitive variables.  The tactile variables where factored separately.  As a result, it is not possible to determine the structural relations between the tactile factors and the five cognitive factors in a manner similar to that of the Stankov group.   The Li et al. (1998) study was focused on exploring the causal relations between sensory abilities and g, not the structural characteristics of cognitive abilities. ]
Olfactory abilities (Go)
Carroll (1993) cited only one study (Jones, 1957) that investigated the structure of the olfactory domain.  Although largely ignored in structural investigations of human cognitive abilities, olfactory abilities are important to study given the use of the olfactory sense by blind or partially sighted people, and experts such as “gourmets, wine connoisseurs, coffee experts, and the like” (Danthiir, Roberts, Pallier, G. & Stankov, 2001, p. 357).    In addition, recent clinical research has suggested that declines in olfactory abilities may be associated with a variety of clinical disorders and diseases ranging from Azheimer’s, idiopathic Parkinson’s, alcoholism and drug abuse, attention deficit/hyperactivity disorders, severe- stage anorexia nervosa, Down’s syndrome, head trauma, multiple sclerosis, restless leg syndrome, seasonal affective disorder, and others (see Doty, 2001, for a complete review)
Carroll’s (1993) analysis of the Jones (1957) olfactory sensitivity data suggested a possible hierarchical structure with four odor-specific narrow abilities (O1, O2, O3, O4) and two unnamed higher-order factors.  More recently, in a study of university students, Danthiir et al. (2001) identified a stratum I  Olfactor Memory (OM) ability that was independent of other higher- order CHC abilities and only weakly related to simple olfactory sensitivity (Stankov, 2000).  Danthiir et al. (2002) concluded that the “OM factor can be considered as part of the taxonomy of cognitive abilities, apparently not dependent on simple olfactory acuity” (p. 355). 
Collectively, the structural research of Carroll (1993) and Danthiir et al. (2002), as well as basic and clinical studies of the olfactory system, suggests that a broad olfactory ability domain (Go) should be included within a comprehensive CHC taxonomy.  Although the Go structural research is sparse, the recent development of sophisticated psychophysical measurement technologies and easy-to-use olfactory function tests, some with relatively large norm samples, will soon likely lead to a better understanding of the cognitive component of Go

[Note.  The interested reader should consult Doty’s (2001) review for information on new olfactory assessment instruments. These include tests such as the 40-odor University of Pennsylvania Smell Identification Test (UPSIT ; known commercially as the Smell Identification Test), the 12-odor Brief-Smell Identification Test (also known as the Cross-Cultural Smell Identification Test), the 3-odor Pocket Smell Test, the 12-item Odor Memory Test, the Odor Confusion Matrix Test, the San Diego Odor Identification Test , the Scandinavian Odor Identification Test, the “Sniff ‘n Sticks” test, the Viennese Olfactory Test Battery, an 8-odor identification test, and the T&T olfactometer test.]