Commentary on Proctor and Wang

Theoretical Issues in Stimulus-Response Compatibility B. Hommel and W. Prinz (Editors) 9 1997 Elsevier Science B.V. All rights reserved.

Commentary on Proctor and Wang Sylvan Komblum University of Michigan, Ann Arbor In this chapter Proctor and Wang examine the relation between set- and element-level compatibility in an attempt to clarify the nature of set-level compatibility. In most of the chapter set-level compatibility is treated as being equivalent to dimensional overlap (see Komblum, Hasbroucq, & Osman, 1990; also Komblum & Lee, 1995). The principal issue addressed is whether set-level compatibility behaves like, and should be treated as, a single unitary concept, or whether it behaves more like a many-faceted concept and should be treated as such. The authors summarize the results of a series of experiments that, they claim, demonstrates that by varying set-level compatibility in different ways, different patterns of interactions are obtained. This, they argue, implies that set-level compatibility (viz., dimensional overlap, or DO) is probably not a unitary concept. In the remarks that follow I comment briefly on Proctor and Wang's exposition of the dimensional overlap model, their data, and their conclusions.

I The Dimensional Overlap Model 'Set-' and 'element-level compatibility' are terms that I have used in describing the literature (see Komblum et al., 1990), but not in talking about the dimensional overlap model 1. The fact that Proctor and Wang use these terms throughout the chapter in discussing the DO model complicates matters if we are to avoid being at cross-purposes. For the sake of the argument, therefore, I draw parallels between our concepts where possible. In the first part of the chapter the authors appear to treat 'set-level compatibility' as conceptually equivalent to 'dimensional overlap, '2 and this is the way I will understand it in my commen1 The DO model has retained the notion of set- and element- level determinants of SRC, but not of set- and element-level compatibility. 2 In the last part of the chapter the authors argue that set-level compatibility is a broader concept than dimensional overlap.

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tary. As for 'element-level compatibility', there is no conceptual equivalent in the DO model; it is, therefore, difficult to discuss this notion in the context of the model. However, operationally, according to the authors, element-level compatibility is manipulated by varying the stimulus-response (S-R) mapping, and is evidenced by reaction time (RT) differences between mapping conditions. The degree of set-level compatibility appears to be operationally defined in terms of the relative values of congruent RTs in different S-R ensembles: Presumably, the faster this RT, the greater the set-level compatibility (i.e., the DO). This is a risky procedure, and not what I originally proposed. It is risky because there are many reasons why the congruent RT in a particular S-R ensemble could differ from that in another ensemble, besides possible differences in the degree of their dimensional overlap: For example, the responses in the one ensemble might take longer to execute than in the other, or the stimuli in the one might be more difficult to discriminate than in the other, etc. It is for this reason that we originally proposed the mapping effectmthat is, the difference between ,the RT of congruent- and incongruent-mapping condit i o n s - a s a possible compatibility metric' (see Kornblum et al., 1990) 3 provided that the correct response in the incongruent mapping condition is identified through search, and not through the application of a rule.

2 The Data The data in this chapter are drawn from three studies conducted by Proctor and his colleagues (Wang & Proctor, 1996, Exp. 1 and 2; Wang & Proctor, in press, Exp. 1, 3, and 4; and Weeks & Proctor, 1990, Exp. 3). All three studies use two-choice tasks in which spatial position is conveyed by the stimuli and expressed by the responses, and in which two or more of the following four, binary-independent variables are manipulated: stimulus modality (spatial/verbal), response modality (spatial/verbal), stimulus orientation (horizontal/vertical), and response orientation (horizontal/vertical); in addition the spatial 'response modality' includes keypresses and aimed movements. Given a particular combination of these variables, the data were collected under two S-R mapping instructions: 'congruent' and 'incongruent. '4 These data have several weaknesses:

3 Because mapping instructions are not expected to have an effect on performance unless there is dimensional overlap, the mapping effect is not a measure of either 'dement-' or 'set-level compatibility' in isolation. However, if one wishes to use these terms, one could think of it as a joint measure. 4 It is true that, empirically, consistent RT differences have been found between mapping conditions when horizontal stimuli are mapped onto vertical responses, or vice-versa (e.g., Bauer & Miller, 1982). This, despite the fact that, on the surface, there does not appear to be any dimensional overlap between up/down and left/right. These

Commentary on Proctor and Wang

41

(1) Because of the many comparisons that the authors make between conditions, it would have been good if the conditions being compared had been included in a factorial design; but they were not. A complete factorial design with these four binary variables would have consisted of sixteen conditions, each run under congruent/compatible and incongruent/incompatible S-R mapping instructions. Of these, only 12 exist among the three studies cited (see Table 1). The four missing conditions are those with spatial, vertical, key-press responses; and if movement responses were considered in addition to keypresses, then the four, spatial, vertical, movement responses are also missing, as are the two, spatial, horizontal, movement responses with vertical stimuli. With the data for these conditions missing, many of the inferences that the authors would like to make are highly constrained. For example, any general inferences involving the interaction between stimulus and response modalities are restricted to conditions with verbal responses; further generalizations (see particularly the first paragraph of the section Theoretical and Methodological Issues) are based on incomplete data. This places severe limitations on the range of valid inferences that can be drawn from these results. (2) While the data for some of the conditions are missing, other conditions are replicated in different experiments. In some cases the results replicate nicely. For example, Wang and Proctor (in press; Table lmA1, A3) and Wang and Proctor (1996; Table l--B2) obtain very similar results in their verbal-verbal, horizontal conditions. However, in other cases there are inexplicable differences between replications. For example, both Weeks and Proctor (1990) and Wang and Proctor (in press) ran conditions with horizontal spatial location stimuli and verbal responses (see Table 1---C3 and A1, A3, respectively). The mapping effect in Weeks and Proctor (Table 1--C3) was close to three times (148 ms) what it was in Wang and Proctor (A1, A3, 41; 50 ms), even though the overall RT was faster in Weeks and Proctor (474 ms) than in Wang and Proctor (584 ms). Thus, the data are not only incomplete but they also appear to be uneven. (3) Yet, some aspects of these data are quite interesting. For example, it is evident that in terms of overall RT, the verbal-verbal S-R conditions are the slowest (about 674 ms), the spatial-spatial (with keypress) the fastest (about 362 ms), and the combined spatial-verbal and verbal-spatial (with keypress), are in-between (516 ms---this, admittedly, is based on incomplete data; however, it

findings may, but need not be, beyond the present scope of the DO model (see Lippa, in press), and are not necessarily problematic. Thus, for example, if the effects of mapping instructions with orthogonal stimulus and response orientations are the result of preferences rather than DO, then the meaning of the terms 'congruent' and 'incongruent' becomes theoretically unclear. Perhaps it would be more appropriate to call S-R mappings in such situations 'compatible' and 'incompatible', instead of 'congruent' and 'incongruent' in order to avoid the theoretical implications of the latter two terms.

TABLE 1 T H E D A T A R E F E R R E D T O BY P R O C T O R

bO AND WANG

SPATIAL RESPONSES (KP#, MOVEMENT*)

VERBAL RESPONSES

HORIZ

Cons H( )RIZ

lncong ME

VERT

Incong ME

VERBAL STIMULI

c~

Co~ H( )RIZ SPATIAL LOCATION STIMULI VERT

Incon8 ME

Cons Inco~ ME

A1

Az

594 746 152 B1 618 670 52

592 747 155

556 597 41 B1 473 510 37

A3 566 616 50

B2 579 741 162 B2 667 717 50 C.3 400 548 148 C3 418 505 87

A. Wang and Proctor (In press)

MEAN 588 745 156 MEAN 618 670 52 MEAN 507 587 80 MEAN 473 510 62

B2

677 716 39 B2 605 779 174 C.3 481 536 55 C3 431 616

185

i AI# 50O 574 74 i! B1 487 5O3 16 "~

AI# 338 405 67

A40 492 560 68

HORIZ MEAN A3* 496 539 637 567 98 , 71

A4* 536 631 95

MEAN 538 634 97

M'EA~I'" 413 454 41

0'3

'A4~

MEAN

A3"

A4"

324 385 61

331 395 64 .,

414 458 44

412 450 38

B1 352 370 18

Cong is Congruent RT

1. S = L/R Location/Words; R = L / R KP/Words

[ncong is Incongruent RT

3. S = L/R as in 1; R = L/R Movements/Words, as in 1

ME is Mapping Effect

4. S = Location/Words; R = KP/Movements

#: Spatial Responses were key presses

B. Wang and Proctor (1996) 1. S = Location (H, V); R = KP (H), Words (H) 2. S = Verbal (H, V); R = Verbal (H, V) C. Weeks and Proctor (1990) 3. S = Location (H, V); R = Verbal (H, V)

*: Spatial Responses were Movements

--

9

<

Commentary on Proctor and Wang

43

is worth noting that the calculated mean of the combined verbal-verbal and spatial-spatial extremes is 518 ms). The range of overall RTs is thus large. What is particularly interesting is that the mapping effects for the horizontal-horizontal (H-H), and vertical-vertical (V-V), verbal-verbal ensembles is 165 ms in contrast to 45 ms for the V-H and H-V (the so-called 'low set-level compatibility' conditions), verbal-verbal ensembles. This is in stark contrast to similar comparisons for the spatial-spatial ensembles (which comparisons are hindered by incomplete data). Even though these are two-choice data, these differences may indicate: First, that the size of the mapping effect is related to the absolute RT--which would pose a problem for our original proposal for a compatibility metric; and/or, second, that there are differences in the way the identity and reversal rules are executed when either the stimuli or the responses are verbal, in contrast to when both are either verbal or spatial. Either of these implications could be of considerable interest.

3 The Conclusions By the time we get to the last section of the chapter, the authors are quite confident that they have demonstrated that, what they call, 'set-level compatibility' displays different functional properties depending on the particular stimulus and response sets in the S-R ensemble: "... We have consistently obtained three different patterns of results for three different types of set-level compatibility manipulations .... " As is clear from my commentary, however, I do not believe that their attempted demonstration is compelling. The logical framework of Proctor and Wang's argument is represented by the six different patterns of interactions between congruent and incongruent RTs that they identify at the beginning of the chapter. These patterns, they contend, reflect different kinds of set-level compatibility. However, the interactions are based on actual RT values rather RT differences between congruent and incongruent mappings (see, also, foomote 4). These 'congruent' RTs are not adequate, by themselves, to distinguish between levels of set-level compatibility, or DO. Imagine two stimulus sets and two response sets whose combinations make up four S-R ensembles. Imagine further that there is an S-R interaction for the congruent RTs in these ensembles. This interaction, by itself, does not necessarily imply that there is a difference in DO between these four ensembles, for such an interaction could easily occur if one of the response sets was related to (i.e., had DO with) the two stimulus sets, and the other not. The only way to distinguish between the related (DO) and unrelated (non-DO) cases is by the mapping effects. If they are not related, then the 'mapping effects' involving the two ensembles with the unrelated response should not differ significantly from each other; if they are related, then the mapping effects in these four ensembles should be different and, in principle, reflect the differences in degrees of DO.

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Sylvan Kornblum

An analysis in terms of congruent RTs only, as proposed by Proctor and Wang, is therefore incomplete. This chapter raises a number of interesting issues. For example" Is dimensional overlap a unitary concept or does it have different functional consequences depending on its basis? What is a reasonable RT-based index of the degree of DO? How does the DO model, or any other model, deal with the effects of S-R mapping with non-overlapping S-R ensembles? These are important issues that need to be addressed if we are to achieve a better understanding of stimulus-response compatibility in the broadest sense of this term.

Author's Note: Funding for this research was provided, in part, by the U.S. Air Force Office of Scientific Research, Grant F49620-94-1-0020. I thank Ling-Po Shiu for useful discussions of the issues.

References Bauer, D. W., & Miller, J. (1982). Stimulus-response compatibility and tile motor system. Quarterly Journal of Experimental Psychology, 34A, 367-380. Komblum, S., Hasbroucq, T., & Osman, A. (1990). Dimensional overlap: Cognitive basis of stimulus-response compatibilityBa model and taxonomy. Psychological Review, 97, 253-170. Komblum, S., & Lee, J.-W. (1995). Stimulus-response compatibility with relevant and irrelevant stimulus dimensions that do and do not overlap with the response.

Journal of Experimental Psychology: Human Perception and Performance, 21, 855-875. Lippa, Y. (in press). A referential-coding explanation for compatibility effects of physically orthogonal stimulus and response dimensions. Quarterly Journal of Experimental Psychology. Wang, H., & Proctor, R. W. (in press). Stimulus-response compatibility as a function of stimulus code and response modality. Journal of Experimental Psychology: Human Perception and Performance. Wang, H., & Proctor, R. W. (1996). Two types of set-level S-R compatibility and their relations with element-level S-R compatibility. Manuscript submitted for publication. Weeks, D. J., & Proctor, R. W. (1990). Salient-features coding in the translation between orthogonal stimulus and response dimensions. Journal of Experimental Psychology: General, 119, 355-366.