SELECTION AND CONTROL OF ACTION
2.2 Action Selection in Single-Task Performance
2.2.2 Stimulus –Response Compatibility Spatial Compatibility SR compatibility refers to the
fact that some arrangements of stimuli and responses, or mappings of individual stimuli to responses, are more natural than others, leading to faster and more accurate responding (see Proctor and Vu, 2006, for a review).
SR compatibility effects were demonstrated by Fitts and colleagues in two classic studies conducted in the 1950s. Specifically, Fitts and Seeger (1953) had subjects perform eight-choice tasks in which subjects moved a stylus (or a combination of two styluses) to a location in response to a stimulus. Subjects performed with each of nine combinations of three display configurations and three control configurations (see Figure 3), using the most compatible mapping of the stimulus and response elements for each combination. The primary finding was that responses were fastest and most accurate when the display and control configurations corresponded spa- tially than when they did not. Fitts and Deininger (1954) examined different mappings of the stimulus and response elements. In the case of circular display and control arrangements (see Figure 3a), performance was much worse with a random mapping of the eight
(a) (b) (c)
Figure 3 Three configurations of stimulus sets and response sets used by Fitts and Seeger (1953). Displays are shown in black boxes, with the stimulus lights shown as circles. Response panels are in gray, with the directions in which one or two styluses could be moved shown by arrows. As an example, an upper right stimulus location was indicated by the upper right light for stimulus set (a), the upper and right lights for stimulus set (b), and the right light of the left pair and upper light of the right pair for stimulus set (c). The upper right response was a movement of a stylus to the upper right response location for response sets (a) and (b), directly for response set (a) and indirectly through the right or upper position for response set (b), or of two styluses for response set (c), one to the right and the other up.
stimulus locations to the eight response locations than with a spatially compatible mapping in which each stim- ulus was mapped to its spatially corresponding response.
This finding demonstrated the basic spatial compatibility effect that has been the subject of many subsequent stud- ies. Almost equally important, performance was much better with a mirror opposite mapping of stimuli to responses than with the random mapping. This finding implies that action selection benefits from being able to apply the same rule regardless of which stimulus occurs.
Spatial compatibility effects also occur when there are only two alternative stimulus positions, left and right, and two responses, left and right keypresses or movements of a joystick or finger, and regardless of whether the stimuli are lights or tones. Moreover, spatial correspondence not only benefits performance when stimulus location is relevant to the task but also when it is irrelevant. If a person is told to press a right key to the onset of a high pitch tone and a left key to onset of a low pitch tone, the responses are faster when the high pitch tone is in a right location (e.g., the right ear of a headphone) than when it is in a left location, and vice versa for the low pitch tone (Simon, 1990). This effect, which is found for visual stimuli as well, is known as the Simon effect after its discoverer, J. R. Simon. The Simon effect and its variants have attracted considerable research interest in the past 15 years because they allow examination of many fundamental issues concerning the relation between perception and action (Proctor, 2011).
Accounts of SR Compatibility Most accounts of SR compatibility effects attribute them to two factors.
One factor is direct, or automatic, activation of the cor- responding response. The other is intentional translation of the stimulus into the desired response according to the instructions that have been provided for the task.
The Simon effect is attributed entirely to the automatic
activation factor, with intentional translation not considered to be involved because stimulus location is irrelevant to the task. The basic idea is that, because the response set has a spatial property, the corresponding response code is activated automatically by the stimulus at its onset, producing a tendency to select that response regardless of whether it is correct. Evidence suggests that this activation may dissipate across time, through either passive decay or active inhibition, because the Simon effect often decreases as RT becomes longer (Hommel, 1993b; De Jong et al., 1994).
In many situations, stimuli can be coded as left or right with respect to multiple frames of reference, as, for example, when there is a row of eight possible stim- ulus positions, four in the left hemispace and four in the right, with each of those divided into left and right pairs and left and right elements within the pairs. In such circumstances, stimulus position is coded relative to all frames of reference, with the magnitude of the Simon effect reflecting the sum of the weighted correspondence effects for each position code (e.g., Lamberts et al., 1992). Errors can result if an inappropriate reference frame is weighted more heavily than one that is relevant to the response, as appears to have been the case in the 1989 crash of a British Midland Airways Boeing 737- 400 aircraft in which the operating right engine was shut down instead of the nonoperating left engine (Learmount and Norris, 1990). Confusion arose about which engine to shut down because the primary instruments for both engines were grouped in a left panel and the secondary instruments for both engines in a right panel, for which the global left and right panels were not mapped com- patibly to the left and right engines (and controls).
SR compatibility proper is also presumed by many researchers to be determined in part by automatic acti- vation of the corresponding response. As for the Simon
SELECTION AND CONTROL OF ACTION 99 effect, the activated response is correct when the map-
ping is compatible and incorrect when the mapping is incompatible. The most influential dual-route model, that of Kornblum et al. (1990), assumes that this auto- matic activation occurs regardless of the SR mapping, a strong form of automaticity. However, certain results question this assumption with regard to compatibility effects (e.g., Read and Proctor, 2009), and more recent treatments of automaticity in general suggest that goal independence is not a defining feature (e.g., Moors and De Houwer, 2006). The intentional translation route is also presumed to play an important role in SR com- patibility effects, with translation being fastest when a “corresponding” rule can be applied, intermediate when some other rule is applicable (e.g., respond at the opposite position), and slowest when there is no simple rule and the specific response assigned to a stimulus must be retrieved from memory.
Dimensional Overlap Although spatial location is an important factor influencing performance, it is by no means the only type of compatibility effect. Kornblum et al. (1990) introduced the term dimensional overlap to describe stimulus and response sets that are percep- tually or conceptually similar. Left and right stimulus locations overlap with left and right response locations both perceptually and conceptually, and responding is fastest with the SR mapping that maintains spatial corre- spondence (left stimulus to left response and right stim- ulus to right response) than with the mapping that does not. The words “left” and “right” mapped to keypress responses also produce a compatibility effect because of the conceptual correspondence between the words and the response dimension, but the effect is typi- cally smaller than that for physical locations due to the absence of perceptual overlap (e.g., Proctor et al., 2002).
SR compatibility and Simon effects have been obtained for a number of different stimulus types with location or direction information, for example, direction of stimulus motion (Galashan et al., 2008) and the direction of gaze of a face stimulus (Ansorge, 2003).
They have also been obtained for typing letters on a keyboard, as a function of the positions in which the letters appear on a computer screen relative to the locations of the keys with which they are typed (Logan, 2003), elements in movement sequences (Inhoff et al., 1984), and clockwise versus counterclockwise rotations of a wheel (Wang et al., 2007). Properties such as the durations of stimuli and responses (short and long;
Kunde and St¨ocker, 2002), positive or negative affective valence of a stimulus in relation to that of a response (Duscherer et al., 2008), and pitch of a tone with that of the vowels in syllable sequences (Rosenbaum et al., 1987) also yield compatibility effects. The point is that compatibility effects are likely to occur for any situation in which the relevant or irrelevant stimulus dimension has perceptual or conceptual overlap with the response dimension.
Influence of Action and Task GoalsIt is important to understand that SR compatibility effects are deter- mined largely by action goals and not the physical responses. This is illustrated by a study conducted by Hommel (1993a) in which subjects made a left or right
keypress to a high or low pitch tone, which could occur in the left or right ear. The closure of the response key produced an action effect of turning on a light on the side opposite that on which the response was made. When instructed to turn on the left light to one tone pitch and the right light to the other, a Simon effect was obtained for which responses were faster when the tone location corresponded with the light location than when it did not, even though this condition was noncorresponding with respect to the key that was pressed. Similarly, when holding a wheel at the bottom, for which the direction of hand movements is incongruent with that of wheel movement, some subjects code the responses as left or right with respect to direction of hand movement and others with respect to direction of wheel movement, and these tendencies can be influenced to some extent by instructions that stress one response coding or the other and by controlled visual events (Guiard, 1983; Wang et al., 2007).
Compatibility effects can occur for situations in which there is no spatial correspondence relation bet- ween stimuli and responses. One such example is when stimulus and response arrays are orthogonal to each other, one being oriented vertically and the other hori- zontally (e.g., Proctor and Cho, 2006). Action selection when there is no spatial correspondence has been studied extensively in the literature on display–control popula- tion stereotypes, in which the main measure of interest is which action a person will choose when operating a control to achieve a desired outcome. Many studies have examined conditions in which the display is linear and the control is a rotary knob. Their results have yielded several principles relating direction of control motion to display movement (Proctor and Vu, 2010b), including:
• Clockwise to Right/Up. Turn the control clock- wise to move the controlled element of the dis- play to the right on a horizontal display or up on a vertical display.
• Clockwise to Increase. Turn the control clock- wise to increase the value of the controlled ele- ment of the display.
• Warrick’s. The controlled element of the display will move in the same direction as the side of the control nearest to the display. This principle is only applicable when the control is to the left or right of a vertical display or below or above a horizontal display.
• Scale Side. The controlled element of the display will move in the same direction as that of the side of the control corresponding to the side of the scale markings on the display.
Performance is most consistent when all stereotypes predict the same response to achieve an action goal.
When the stereotypes are in conflict (e.g., the clockwise- to-right principle specifies clockwise rotation, whereas Warrick’s principle specifies counterclockwise rotation), choices are less consistent across individuals and group differences from experience become more evident. For example, Hoffmann (1997) reported that psychology
students abide more by the clockwise-to-right principle, whereas engineering students tend to adhere to War- rick’s principle.