The role of attention for the Simon effect

Summary It has been claimed that spatial attention plays a decisive role in the effect of irrelevant spatial stimulus-response correspondence (i. e., the Simon effect), especially the way the attentional focus is moved onto the stimulus (lateral shifting rather than zooming). This attentional-movement hypothesis is contrasted with a referential-coding hypothesis, according to which spatial stimulus coding depends on the availability of frames or objects of reference rather than on certain attentional movements. In six experiments, reference objects were made available to aid spatial coding, which either appeared simultaneously with the stimulus (Experiments 1–3), or were continuously visible (Experiments 4–6). In contrast to previous experiments and to the attentional predictions, the Simon effect occurred even though the stimuli were precued by large frames surrounding both possible stimulus positions (Experiment 1), even when the reference object's salience was markedly reduced (Experiment 2), or when the precueing frames were made more informative (Experiment 3). Furthermore, it was found that the Simon effect is not reduced by spatial correspondence between an uninformative spatial precue and the stimulus (Experiment 4), and it does not depend on the location of spatial precues appearing to the left or right of both possible stimulus locations (Experiment 5). This was true even when the precue was made task-relevant in order to ensure attentional focusing (Experiment 6). In sum, it is shown that the Simon effect does not depend on the kind of attentional operation presumably performed to focus onto the stimulus. It is argued that the available data are consistent with a coding approach to the Simon effect which, however, needs to be developed to be more precise as to the conditions for spatial stimulus coding.     

Is rapid performance improvement across short precue-target delays due to masking from peripheral precues?

The role of lateral masking in more rapid performance improvement with peripheral than with central precuing was investigated. A peripheral precue to the inside of the target location provided less masking at zero precue-target delay than a precue to the outside (experiment 1) or a precue involving a partial target at the target location (experiment 2). There was no significant interaction between precue-target delay and precue type in a comparison of inside precues and precues involving a briefly-brightened box around the target location, although overall performance was significantly poorer with the latter (experiment 3). Performance was better at short precue-target delays with inside precues than with central precues (experiment 4), yet it did not improve significantly more rapidly. Minimizing lateral masking with peripheral precues thus eliminates the dramatic performance improvement sometimes observed across short precue-target delays, causing performance to be consistently better than with central precues across these delays.     

A shift of attention may be necessary, but it is not sufficient, for the generation of the Simon effect

The Simon effect is the performance advantage for spatially corresponding, compared to non-corresponding, target-response ensembles when the location of the target is task irrelevant. In four experiments, we tested the predictions of the attention-shift account of the Simon effect. In all experiments, subjects made choice responses with respect to the identity of a central target that followed a spatially non-informative peripheral precue. The first experiment showed a Simon effect away from the precue when the precue was a go/no-go signal: responses to spatially non-corresponding precue-response pairs were faster than responses to spatially corresponding precue-response pairs. The results of the second experiment suggested that this “reverse” Simon effect was not due to inhibition. In the third experiment, a secondary working memory task required the encoding, and later recall, of “oddball” precues. Although the Simon effect was absent, larger Simon effects towards the precue (i.e., responses were faster to spatially corresponding, compared to non-corresponding, precue-response ensembles) were correlated with poorer performance on the memory task. In the last experiment, the identity of completely non-informative precues was congruent, incongruent, or unrelated to the identity of the target. With precues that were unrelated to the identity of the target, there was a Simon effect towards the precues. Conversely, the Simon effect occurred away from the precue when the identity of the precue was related to that of the target. The findings suggest that a shift of attention alone is not sufficient to produce the Simon effect. Rather, the shift of attention must originate from an intentionally defined object. The results are discussed within a framework that integrates the attention-shift and referential-coding hypotheses. Received: 2 December 1999 / Accepted: 23 March 2000     

Attention precuing and Simon effects: A test of the attention-coding account of the Simon effect

Simon effects refer to the finding that choice-response latencies to a nonspatial aspect of a stimulus vary depending on the spatial correspondence between the stimulus position and the position of the correct response alternative. Recently, researchers have proposed an attention-coding account of Simon effects whereby the (irrelevant) stimulus spatial code involved in the generation of the effect is formed in the process of attentional orienting to the stimulus. This account predicts that if attentional orienting is unnecessary at stimulus onset, as when the stimulus appears at an attended location, Simon effects will not be observed. This prediction was tested by measurement of Simon effects in an attention-precuing task in which the stimulus was presented at attended and unattended locations. Significant Simon effects were observed independently of the focus of attention. This result was obtained over a large range of precue-target SOAs, and did not depend on whether central or peripheral precues were used to direct attention or on whether the relevant target dimension was color or form. Significant Simon effects were not observed when the precue-target SOA was 50 ms, irrespective of the other precue and task conditions. The data do not support the prediction of the attention-coding account and thus question the generality of the account in its current form. It is suggested that spatial and temporal uncertainties are important factors that influence the pattern of results, and that these factors must be incorporated into attention-coding models of the Simon effect.     

Effects of spatial and symbolic precues on localization performance

One of the fundamental properties of spatial vision is the ability to localize objects in space. According to a recent proposal, accurate localization performance involves the operation of two systems: the attention system and the eye movement system. Upon stimulus presentation, attention is shifted to the target area: this provides coarse location information. Subsequently, a saccadic eye movement is executed: this provides fine location information. In this study we tested predictions derived from this model concerning the effects of precue information on localization performance. In a series of five experiments we manipulated duration of precue (71, 400, and 1,000 ms) and type of precue (spatial versus symbolic). Results showed that very short duration (i.e., 71 ms) spatial precues improved localization performance whereas very short duration symbolic precues did not. In contrast, the 1,000 ms duration precue condition showed similar amounts of precuing benefit for the spatial and symbolic precues. This pattern of differential precuing effects corroborated the two-process model of localization performance. Received: 24 June 1999 / Accepted: 28 January 2000     

Are movements prepared in parts? Not under compatible (naturalized) conditions

This set of experiments is concerned with the specification of movement parameters hypothesized to be involved in the initiation of movement. Experiment 1 incorporated the precuing method developed by Rosenbaum in which a precue provided partial information of the upcoming movement before the stimulus to move. Under conditions in which precues were provided by letter symbols and stimuli were color-coded dots mapped to response keys. Rosenbaum found reaction times to be slower for the specification of arm than for direction, and both to be slower than the specification of extent. In Experiment 1, using precue and stimulus conditions that paralleled those employed by Rosenbaum, we obtained very similar findings. The three follow-up experiments extended these findings to more naturalized stimulus-response compatible conditions. We used a method in which precues and stimuli were directly specified through vision and mapped in a one-to-one manner with responses. In Experiment 2, although reacion times decreased as a function of the number of parameters precued, there were no systematic effects of precuing particular parameters. In Experiments 3 and 4, we incorported an ambiguous precue that, while serving to reduce task uncertainty, failed to provide any specific information as to the arm, direction, or extent of the upcoming movement. Initiation times did not systematically vary as a function of the type of parameter precued nor were there significant differences between specific and ambiguous precue conditions. In sum, only in Experiment 1 in which precues and stimuli involved complex cognitive transformations was there support for Rosenbaum's parameter specification model. When we employed highly compatible conditions, designed to reflect a real-world environment, we failed to obtain any tendency for movement parameters to be serially specified. We discuss grounds for suspecting the generality of parameter specification models and propose an alternative approach that is consonant with the dynamic characteristics of the motor control system.     

Intentional pre-cueing does not influence the Simon effect

Choice reactions can be performed more quickly if the response corresponds spatially to the stimulus, even when the stimulus location is irrelevant for the task (Simon effect). It is assumed that the Simon effect is related to interference between spatial stimulus and response codes in a response selection stage. A central finding for such a response selection account is the increase in the effect if the most probable response location is given in advance by an intentional pre-cue. However, Hasbroucq and Possamaï (1994) assumed that the increase in the Simon effect in such a task may be due to an unmeant pre-cueing of the stimulus location, which has been recently supported by an electroencephalography (EEG) study by Wascher and Wolber (2004). In the present study this notion has been tested experimentally. In Experiment 1, a centrally presented symbolic cue served as an intentional cue. As a result, the enhancement of the Simon effect in valid cueing almost disappeared. When tactile cues were used (Experiment 2), the increase in the Simon effect disappeared completely. Thus, the influence of intentional cueing reported in previous studies can be assigned to attentional factors and does not support a response selection account.     

Attentional and intentional cueing in a Simon task: An EEG-based approach

Advance information about the location of a stimulus (attentional cueing) does not affect the Simon effect (a shortening of manual response times whenever the position of a stimulus that is irrelevant for the task corresponds to the side of the response). However, advance information about the side of a response (intentional cueing) enhances the Simon effect. At first sight, these well-established results contradict two important assumptions about the origin of the Simon effect: (a) the effect originates at least in part in a covert shift of visual attention that forces the preparation of a response towards the location of the attentional shift and (b) interference between stimulus location and response side takes place within a response selection stage. We replicated the behavioral finding in a study that measured event-related potentials (ERPs) of the EEG. ERPs indicated that the mechanisms causing the Simon effect remain widely unaffected by advance information. Clear evidence for both response preparation and attentional shifts in the cue-target interval was found. Additionally, ERPs suggested that the increment of the Simon effect by intentional cueing might be due to perceptual factors rather than to an alteration in the mechanisms involved in the generation of a regular Simon effect. The implications of these data for the role of attention and of response selection in Simon tasks are discussed.     

Mixing location-relevant and location-irrelevant choice-reaction tasks: influences of location mapping on the Simon effect

The Simon effect refers to the finding that reaction times are faster when stimulus and response locations correspond than when they do not in tasks where stimulus location is defined as irrelevant. The authors examined the Simon effect for situations in which location-irrelevant trials were intermixed with trials for which stimulus location was relevant. Compatible mapping of the location-relevant trials enhanced the Simon effect relative to an unmixed condition, whereas incompatible mapping reversed the Simon effect. The reversal with incompatible mapping remained evident when task uncertainty was removed by use of a precue and was larger than the reversed effect produced by making incongruent trials more frequent than congruent trials. This result suggests that both attentional biases and task-defined associations contribute to the reversal of the Simon effect.     

Large and rapid improvement in form discrimination accuracy following a location precue

Processing of a visual stimulus can be improved by precuing its location. Most previous precue studies have used reaction time as the dependent measure and have found large effects; but when form discrimination accuracy has been used, precue effects have been relatively small. The present experiments yielded large, short-latency precue effects on form discrimination accuracy. A small square precue was briefly presented near one of four possible target locations. Then one of four possible targets (T-like figures) was presented in each location, followed by a mask. Observers attempted to identify the target that had been presented in the cued location. In experiment 1, target duration, cue-to-target distance, and cue-target onset asynchrony (SOA) were varied. Target discriminability (d') increased markedly with increasing precue-target SOA, even at very short SOAs. Thus, there was no evidence for a delay in the onset of precue effects (caused, for example, by the need to shift attention across the visual field). Performance was best for precues that were closest to the target, thus ruling out a forward masking explanation of the effect. Finally SOA and target duration interacted strongly - longer precue SOAs resulted in larger effects of target duration. In experiment 2, this interaction was replicated using an additional target duration and longer SOAs. One interpretation of this result is that focal attention increases the rate at which information can be extracted from a visual location.     

The functional role of attention for spatial coding in the Simon effect

Summary Two experiments investigated relative spatial coding in the Simon effect. It was hypothesized that relative spatial coding is carried out with reference to the position of the focus of visual attention. The spatial code for an imperative stimulus presented exactly at the position of focal attention should be neutral on the horizontal plane, and therefore no Simon effect should be observed. However, when the imperative stimulus is presented to the left or to the right of the current position of focal attention, the spatial code should not be neutral, thus producing a Simon effect. In both experiments, focal attention was manipulated either by a peripherally presented onset precue (Experiment 1) or by a centrally presented symbolic precue (Experiment 2). Results showed that the Simon effect was substantially reduced in both experiments when a valid precue preceded the imperative stimulus just in time to conclude refocusing of attention to the position of the imperative stimulus before it was presented. However, conditions with neutral precues yielded a normally sized Simon effect. In both experiments, the Simon effect decreased as the SOA grew when the precue was valid. At least for the Simon effect, the results can be interpreted as evidence that relative spatial coding is functionally related to the position of the focus of attention.     

Influences of presentation mode and time pressure on the utilisation of advance information in response preparation.

An important approach to the investigation of movement selection and preparation is the precuing paradigm where preliminary information about a multidimensional response leads to reaction time benefits which are positively related to the amount of precue information. This so-called precuing effect is commonly attributed to data-limited preparatory motoric processes performed in advance of the response signal. By means of recording the lateralised readiness potential (LRP), the present experiments investigated whether the precuing effect could be explained also by variables that affect strategic utilisation of stimulus-conveyed information. Experiment 1 presented fully and partially informative precues either in mixed or blocked mode. Experiment 2 exerted various degrees of time pressure to the different precue conditions. In both experiments, the precuing effect on reaction times and the LRP was fully preserved, refuting the notion that the sensitivity of the LRP to the amount of preliminary information merely reflects differential precue utilisation. As a major finding, time pressure increased the LRP amplitude during response preparation which is consistent with the view that response strategies generally influence movement preparation on a motoric level.     

The Role of Precues in the Preparation of Motor Responses in Humans

The authors investigated how precues about the location of an upcoming target are used by the sensorimotor system to reduce manual reaction time. In 4 experiments, participants (N = 12 in each experiment) pressed a response key as fast as possible when a precued or a nonprecued visual target appeared. Precues remained effective when a visual mask was interposed between the display of the precue and the target (Experiment 1), which suggests that precues act downstream from visual sensory memory. The precue effect was abolished when precues were presented along with a task requiring attention and a verbal response (Experiment 2) but not when presented with a task that required verbal output but had no attention demands (Experiment 3). Those findings indicate that precues must be processed attentively to become effective. When the attention-demanding task was interposed between precue and target display, the precue effect was still abolished (Experiment 4), which suggests that individuals' attention must remain in the precued area until target appearance.     

Reaction Time Methods in the Study of Motor Programming

Recent reaction time analysis of motor programming has utilized a precue stimulus that provides advance information about some or all of the attributes for the upcoming motor response. This kind of precue typically confounds the number of remaining stimuli with the motoric processes under investigation (Zelaznik, 1978). In Experiments 1 and 2 the precuing of hand, digit, and duration of a key press response was manipulated. A new precuing procedure was utilized that does not confound the number of stimuli with the motoric processes under investigation. The findings of Experiments 1 and 2 demonstrate that none of the advance information was helpful in reducing reaction time and as such, suggest that these features of movement are not selected in any particular order. Experiment 3 compared this new method of precuing to the older, traditional method. The results of this experiment suggested that there is parallel processing of the perceptual and motor mental operations in this reaction-time task, since there was an underadditive interaction between the number of stimulus response alternatives and the non-precued movement dimensions. This paper highlights problems inherent in the utilization of precuing methods to understand motor programming processes. It appears that a better understanding about the variables involved in movement control is necessary before examining the order of selection of those variables.     

Reaction time methods in the study of motor programming: the precuing of hand, digit, and duration

Recent reaction time analysis of motor programming has utilized a precue stimulus that provides advance information about some or all of the attributes for the upcoming motor response. This kind of precue typically confounds the number of remaining stimuli with the motoric processes under investigation (Zelaznik, 1978). In Experiments 1 and 2 the precuing of hand, digit, and duration of a key press response was manipulated. A new precuing procedure was utilized that does not confound the number of stimuli with the motoric processes under investigation. The findings of Experiments 1 and 2 demonstrate that none of the advance information was helpful in reducing reaction time and as such, suggest that these features of movement are not selected in any particular order. Experiment 3 compared this new method of precuing to the other, traditional method. The results of this experiment suggested that there is parallel processing of the perceptual and motor mental operations in this reaction-time task, since there was an underadditive interaction between the number of stimulus response alternatives and the non-precued movement dimensions. This paper highlights problems inherent in the utilization of precursing methods to understand motor programming processes. It appears that a better understanding about the variables involved in movement control is necessary before examining the order of selection of those variables.     

Hand-hemispace spatial compatibility,precueing, and stimulus-onset asynchrony

Summary The role of attention and the resolution of coding conflicts in hand-hemispace spatial-compatibility effects was examined in a precueing experiment in which visual and vibrotactile precues, with various stimulus-onset asynchronies (SOAs), were presented in blocked and random order. It was expected that precues at the shorter SOAs would fail to facilitate the shifting of attention, as they occur too close to the imperative stimulus to be informative. The task would therefore approximate one of choice reaction time (RT), resulting in a hand-hemispace spatial-compatibility effect. Conversely, the longer SOAs would provide the subject with sufficient time in which to shift attention fully, and would therefore result in a task more like that of simple reaction time (SRT). It was expected that the hand-hemispace spatial-compatibility effect would then be absent. As was expected, this effect was present at the shorter SOAs, and absent at the longer SOAs. In Experiments 2 and 3, provision of a visual precue further facilitated attentional deployment, as did blocking the presentation of various SOAs in Experiment 3. Vibrotactile and visual precues did not differ in their ability to direct attention, implying that these modalities orient attention and precue location in essentially similar ways. These findings are discussed within the context of the mechanisms thought to underlie the time course of spatial compatibility and the dissipation of a fading trace of interfering spatial codes.     

Attention effects of abrupt-onset precues with central, single-element, and multiple-element precues

Endogenous and exogenous processes of attention have been inferred with different types of precues used in allocation of attention to a target location. In the present research, a comparison was made between the typical peripheral single-element precue (SEP), a central precue, and a multiple-element precue (MEP) in order to further understanding of the processes involved in allocation of attention. Two precues were used on each trial in these experiments. An abrupt-onset precue appeared with an SEP, an MEP, or a central precue and was followed 50 or 300 ms later by a screen containing a target and two distractor characters. The abrupt-onset precue and the other precue each could be valid or invalid in indicating the location of the target, as in the study by Juola, Koshino, and Warner (1995). Response times to the targets showed that validity effects of the abrupt-onset precue and the MEP or central precue were additive, whereas those of the abrupt-onset precue and the SEP were interactive. These data suggest that, like a central precue, an MEP is an endogenous precue that guides conscious control of attention and has its attentional effects at a different processing level from an SEP, which is an exogenous precue and may compete for attentional resources with an abrupt-onset precue.     

The scaling of spatial attention in visual search and its modification in healthy aging

A model of visual search (Greenwood & Parasuraman, 1999) postulating that visuospatial attention is composed of two processing components--shifting and scaling of a variable-gradient attentional focus--was tested in three experiments. Whereas young participants are able to dynamically constrict or expand the focus of visuospatial attention on the basis of prior information, in healthy aging individuals visuospatial attention becomes a poorly focused beam, unable to be constricted around one array element. In the present work, we sought to examine predictions of this view in healthy young and older participants. An attentional focus constricted in response to an element-sized precue had the strongest facilitatory effect on visual search. However, this was true only when the precue correctly indicated the location of a target fixed in size. When precues incorrectly indicated target location or when target size varied, the optimal spatial scale of attention for search was larger, encompassing a number of array elements. Healthy aging altered the deployment of attentional scaling: The benefit of valid precues on search initially (in participants 65-74 years of age) was increased but later (in those 75-85 years of age) was reduced. The results also provided evidence that cue size effects are attentional, not strategic. This evidence is consistent with the proposed model of attentional scaling in visual search.     

Oculomotor readiness and covert orienting: Differences between central and peripheral precues

The costs produced by invalid precues can depend on the spatial relationship between the cued location and the target location. If oculomotor programs mediate attention shifts, then the effect of varying the spatial relation between the cue and target should be the same for covert orienting (indexed by manual responses) and saccadic responses. We found this to be true only for central precues. With central precues, both manual and saccadic costs were greater when cue and target occurred on opposite sides of the vertical meridian than when they occurred on the same side. With peripheral precues, there were no meridian effects in either response condition, but there was a significant dissociation in the pattern of saccadic and manual costs. For manual responses costs were greater when the target was eccentric relative to the cue, whereas for saccades costs were greater when the cue was eccentric to the target. These results provide additional support for the idea that different orienting mechanisms are engaged by central and peripheral precues. They further suggest that the relationship between oculomotor and attentional orienting may depend on the nature of the precue, with the potential for interdependence being greater with central precues.     

Attention effects of moving and stationary single-element and multiple-element precues: Limits of automaticity

A multiple-element precue (MEP), in which one unique element defines the actual precue, results in efficient precuing for identification of a target. The time course for identification in this case is similar to that for a central precue, even though it is presented peripherally (Chastain, 1996; Chastain & Cheal, in press). Five experiments were conducted to gain further information on the function of MEPs and to question what advantage prior knowledge of the precue may give. In Experiments 1 and 2, it was shown that for “pop-out” features, accuracy of identification of a target was higher if the precue type was known in advance. In contrast, as shown in Experiments 3, 4, and 5, when the precue was defined by apparent motion, there was no difference in accuracy due to advanced knowledge of the precue. Further, accuracy was considerably better for motion precues than for stationary precues.