Practice effects vs. transfer effects in the Simon task.

The Simon effect refers to the fact that, even though stimulus position is task-irrelevant, responses to a task-relevant stimulus dimension are faster and more accurate when the stimulus and response spatially correspond than when they do not. Although the Simon effect is a very robust phenomenon, it is modulated by practice or transfer from previous tasks. Practice refers to the modulation of the Simon effect as a function of number of trials. Transfer refers to the modulation of the Simon effect as a function of preceding tasks. The aim of the present study is to disentangle the role of practice and transfer in modulating the Simon effect and to investigate whether such modulation can be extended to a different response modality. Three experiments were conducted, which included three sessions: the Baseline session, the Inducer session and the Diagnostic session. The task performed in the Baseline and the Diagnostic sessions were comprised of location-irrelevant trials (i.e., they were Simon tasks). The task performed in the Inducer session required performing location-relevant trials (i.e., it was a spatial compatibility task with a compatible or an incompatible stimulus-response mapping). In the first and third experiments, participants were required to respond manually in all sessions. In the second experiment, the task performed in the Inducer session required manual response, while in the Baseline and Diagnostic sessions the tasks required ocular response. Results showed a reduced-Diagnostic Simon effect after both compatible and incompatible mapping in the Inducer session, regardless of whether response modality was the same or different. These results support the notion that the practice effect prevails over the transfer effect.

Sequential modulation of (bottom-up) response activation and inhibition in a response conflict task: a single-pulse transcranial magnetic stimulation study.

Many cognitive tasks involve a response conflict between the response selected on the basis of the task-relevant attribute and that primed by an irrelevant attribute. Although response priming has been extensively investigated, we still have little evidence on whether it entails both excitatory and inhibitory processes and the way in which these processes are modulated by the prior occurrence of a conflict between-response alternatives. To shed light on these issues, we tested motor cortex excitability during a two-choice compatibility task (a Simon task) by delivering single pulses of transcranial magnetic stimulation and recording the resulting motor evoked potentials (MEPs). We obtained consistent behavioural and MEP results suggesting that the presentation of a left- or right-side stimulus causes the activation of the ipsilateral response, which-in turn-inhibits the alternative response. Both processes are modulated by the spatial compatibility of the preceding trial. In trials following compatible trials (i.e. after conditions wherein the primed response was the correct one), we found response efficiency advantages and disadvantages of compatible and incompatible trials, respectively, which were mirrored by an increase of the excitability of the motor cortex primed by stimulus position and by a parallel decrease of the contralateral cortex excitability. Both the facilitation and interference components of the behavioural effect and the excitatory and inhibitory effects of the stimulus position on motor excitability were smaller after neutral trials (i.e. when the stimulus of the previous trial was aligned with fixation, thus not priming any response) and absent after incompatible trials (i.e. after having experienced a conflict between the primed and correct responses). These results are consistent with the idea that location-based response priming is under control of a conflict monitoring mechanism that strengthens ipsilateral response activation and contralateral response inhibition after compatible trials and weakens both processes after incompatible trials.

Role of stimulus and response feature overlap in between-task logical recoding.

The reversal logical recoding rule (i.e., "respond opposite") induced by an incompatible task (e.g., a task requiring to respond to red or green stimuli by pressing a key of the alternative colour compared to that of the stimulus) can be transferred to another task when the two tasks are combined in a task-switching paradigm. When the task to which the rule is transferred is a Simon task, this causes the disappearance of the typical advantage for responses that spatially correspond to the stimulus, or even results in an advantage for spatially noncorresponding responses. The present study aimed at investigating whether the transferred rule is independent of the specific stimulus and response dimensions for which it has been created. Previous studies suggest that when a Simon task is coupled with a colour incompatible task, the Simon effect may disappear or reverse even when stimuli in the two tasks, apart from being both visual and appearing on the same computer screen, have no other features in common. Results of the present study corroborate the hypothesis that feature overlap between stimuli is not necessary for the between-task transfer of the logical rule. However, an overlap between the representations of responses appears to be crucial. No modulation of the Simon effect was observed when the Simon task required bimanual responses while the colour-compatibility task required either vocal responses or responses executed with the two feet. In contrast, we did observe such a modulation when the discriminative response dimension and the effectors/response device were the same in the two tasks, even though these two tasks provided for different stimuli.

The Spatial Representation of Angles.

We investigated whether angle magnitude, similarly to numerical quantities (i.e., the spatial-numerical association of response codes effect), is associated to the side of response execution. In addition, we investigated whether this association has the properties of a spatially oriented mental line, since angles are taught in a right-to-left progression. We tested two groups of participants: civil engineering students (high familiarity with angles) and psychology students (low familiarity with angles). In Experiment 1, participants were asked to judge the continuity of the angles' arms (continuous vs. dashed). Magnitude of the angles was task-irrelevant. In Experiment 2, they were asked to judge whether the presented angles were smaller or larger than a right angle (90°). Therefore, the angle magnitude was relevant for performing the task. Overall, engineering students responded faster with their left hand to large angles and with their right hand to small angles. Conversely, psychology students did not show any reliable differences between left- and right-hand responses. In the case of engineering students, the spatial association has a right-to-left (counter clockwise) direction, suggesting the influence of education and practice on the mental representation of angle magnitude.

Living on the edge: strategic and instructed slowing in the stop signal task.

The stop signal task is widely adopted to assess motor inhibition performance in both clinical and non-clinical populations. Several recent studies explored the influence of strategic approaches to the task. In particular, response slowing seems to be a strategic approach commonly adopted to perform the task. In the present study, we compared a standard version with a strategic version of the task, in which participants were explicitly instructed to slow down responses. Results showed that the instructed slowing did not affect the main inhibition measure, thus confirming the robustness of the stop signal index. On the other hand, it apparently changed the nature of the task, as shown by the lack of correlation between the standard and the strategic versions. In addition, we found a specific influence of individual characteristics on slowing strategies. In the standard version, adherence to task instructions was positively correlated with compliant traits of personality. Despite instructions to maximize response speed, non-compliant participants preferred to adopt a slowing strategy in the standard version of the task, up to a speed level similar to the strategic version, where slowing was required by task instructions. Understanding the role of individual approach to the task seems to be crucial to properly identify how participants cope with task instructions.

Difficulty matters: unspecific attentional demands as a major determinant of performance highlighted by clinical studies.

The cognitive impairments shown by brain-damaged patients emphasize the role of task difficulty as a major determinant for performance. We discuss the proposal of Kurzban et al. in light of our findings on right-hemisphere-damaged patients, who show increasing awareness deficits for the contralesional hemispace when engaged with resource-consuming dual tasks. This phenomenon is readily explained by the assumption of unspecific depletable resources.

Paying attention through eye movements: a computational investigation of the premotor theory of spatial attention.

Growing evidence indicates that planning eye movements and orienting visuospatial attention share overlapping brain mechanisms. A tight link between endogenous attention and eye movements is maintained by the premotor theory, in contrast to other accounts that postulate the existence of specific attention mechanisms that modulate the activity of information processing systems. The strong assumption of equivalence between attention and eye movements, however, is challenged by demonstrations that human observers are able to keep attention on a specific location while moving the eyes elsewhere. Here we investigate whether a recurrent model of saccadic planning can account for attentional effects without requiring additional or specific mechanisms separate from the circuits that perform sensorimotor transformations for eye movements. The model builds on the basis function approach and includes a circuit that performs spatial remapping using an "internal forward model" of how visual inputs are modified as a result of saccadic movements. Simulations show that the latter circuit is crucial to account for dissociations between attention and eye movements that may be invoked to disprove the premotor theory. The model provides new insights into how spatial remapping may be implemented in parietal cortex and offers a computational framework for recent proposals that link visual stability with remapping of attention pointers.

Dissociation between awareness and spatial coding: evidence from unilateral neglect.

Prevalent theories about consciousness propose a causal relation between lack of spatial coding and absence of conscious experience: The failure to code the position of an object is assumed to prevent this object from entering consciousness. This is consistent with influential theories of unilateral neglect following brain damage, according to which spatial coding of neglected stimuli is defective, and this would keep their processing at the nonconscious level. Contrary to this view, we report evidence showing that spatial coding and consciousness can dissociate. A patient with left neglect, who was not aware of contralesional stimuli, was able to process their color and position. However, in contrast to (ipsilesional) consciously perceived stimuli, color and position of neglected stimuli were processed separately. We propose that individual object features, including position, can be processed without attention and consciousness and that conscious perception of an object depends on the binding of its features into an integrated percept.

Fine-grained pitch processing of music and speech in congenital amusia.

Congenital amusia is a lifelong disorder of music processing that has been ascribed to impaired pitch perception and memory. The present study tested a large group of amusics (n=17) and provided evidence that their pitch deficit affects pitch processing in speech to a lesser extent: Fine-grained pitch discrimination was better in spoken syllables than in acoustically matched tones. Unlike amusics, control participants performed fine-grained pitch discrimination better for musical material than for verbal material. These findings suggest that pitch extraction can be influenced by the nature of the material (music vs speech), and that amusics' pitch deficit is not restricted to musical material, but extends to segmented speech events.

A Simon effect for depth in three-dimensional displays.

We investigated whether the Simon effect occurs for the depth dimension in a 3-dimensional display. In Experiment 1, participants executed discriminative responses to 2 stimuli, a cross and a sphere, both 3-dimensional, which were perceived to be located near or far with respect to the participant's body. The response keys were located near and far along the participant's midline. Apparent stimulus spatial location (near or far) was irrelevant to the task. Results showed a depth Simon effect, attributable to the apparent stimulus spatial location. Experiment 2 replicated Experiment 1 with a different procedure. The 2 stimuli, a triangle and a rectangle, were 2-dimensional and were perceived as being located near or far from the participant's midline; the response keys were located near and far along the participant's midline. Results showed again the depth Simon effect. Experiment 3 was a control condition in which the 2 stimuli, drawings of a lamp and of a chair, had the same size, regardless of whether they appeared to be near or far. The depth Simon effect was replicated. A distribution analysis on data of Experiment 3 showed that the Simon effect increased as reaction times became longer. In Experiment 4, the position of the 2 stimuli, a circle and a cross, varied on the horizontal (right or left) dimension, whereas the position of the 2 responses varied along the depth (near or far) dimension. No Simon effect was found.

Attentional distractor interference may be diminished by concurrent working memory load in normal participants and traumatic brain injury patients.

A reduction in congruency effects under working memory (WM) load has been previously described using different attentional paradigms (e.g., Kim, Kim, & Chun, 2005; Smilek, Enns, Eastwood, & Merikle, 2006). One hypothesis is that different types of WM load have different effects on attentional selection, depending on whether a specific memory load demands resources in common with target or distractor processing. In particular, if information in WM is related to the distractors in the selective attention task, there is a reduction in distraction (Kim et al., 2005). However, although previous results seem to point to a decrease in interference under high WM load conditions (Kim et al., 2005), the lack of a neutral baseline for the congruency effects makes it difficult to differentiate between a decrease in interference or in facilitation. In the present work we included neutral trials in the task introduced by Kim et al. (2005) and tested normal participants and traumatic brain injury patients. Results support a reduction in the processing of distractors under WM load, at least for incongruent trials in both groups. Theoretical as well as applied implications are discussed.

A SNARC-like effect for music notation: The role of expertise and musical instrument.

The Spatial-Numerical Association of Response Codes (SNARC) suggests the existence of an association between number magnitude and response location, with faster left key-press responses to small numbers and faster right key-press responses to large numbers. We investigated whether a similar association exists between musical notes on the stave and the space of response execution, involving amateur and expert musicians (Experiment 1). Moreover, in Experiment 2 we further investigated such association in two groups of expert musicians (piano and transverse flute players) who differ in the note mapping on their instruments. Results indicate a clear association between musical notes and the space of response execution only for musicians with formal education. Furthermore, this association seems not to be influenced by the specific instrument played, as both piano and transverse flute players showed the same effect direction (left key-press advantage for low notes, and vice versa).

The spatial representation of numbers: evidence from neglect and pseudoneglect.

The aim of the present paper is to provide an overview of the evidence that links spatial representation with representation of number magnitude. This aim is achieved by reviewing the literature concerning the number interval bisection task in patients with left hemispatial neglect and in healthy participants (pseudoneglect). Phenomena like the Spatial Numerical Association of Response Codes (SNARC) effect and the shifts of covert spatial attention caused by number processing are thought to support the notion that number magnitude is represented along a spatially organized mental number line. However, the evidence provided by chronometric studies is not univocal and is open to alternative, non-spatial interpretations. In contrast, neuropsychological studies have offered convincing evidence that humans indeed represent numbers on a mental number line oriented from left to right. Neglect patients systematically misplace the midpoint of a numerical interval they are asked to bisect (e.g., they say that [5] is halfway between [2] and [6]) and their mistakes closely resemble the typical pattern found in bisection of true visual lines. The presence of dissociations between impaired explicit knowledge and spared implicit knowledge supports the notion that neglect produces a deficit in accessing an intact mental number line, rather than a distortion in the representation of that line. Other results show that the existence of a strong spatial connotation constitutes a specific property of number representations rather than a general characteristic of all ordered sequences.

Perceptual and attentional factors in encoding irrelevant spatial information.

Numerous studies found superior performance when the irrelevant location of a stimulus and response location were corresponding than when they were not corresponding (Simon effect), suggesting that stimulus location is processed in an obligatory manner. The present study compared Simon effects from the location of a relevant (i.e., to-be-attended) object to those from the location of an irrelevant (i.e., to-be-ignored) object. In four experiments, participants were presented with a rectangular frame and a square, with the relevant object in green or red color and the irrelevant object in gray or white color. Participants' task was to respond with a lateral keypress to the color of the relevant object, and we varied spatial correspondence between the location of the relevant or the irrelevant object and the response, respectively. Results consistently showed larger Simon effects from the location of the relevant than from the irrelevant object, even when the irrelevant object was made very salient. These results suggest that location processing is largely confined to relevant (i.e., attended) objects, stressing the role of attention shifts for location encoding.

Response selection and attention orienting: a computational model of Simon effect asymmetries.

Recently, there has been a redirection of research efforts toward the exploration of the role of hemispheric lateralization in determining Simon effect asymmetries. The present study aimed at implementing a connectionist model that simulates the cognitive mechanisms implied by such asymmetries, focusing on the underlying neural structure. A left-lateralized response-selection mechanism was implemented alone (Experiment 1) or along with a right-lateralized automatic attention-orienting mechanism (Experiment 2). It was found that both models yielded Simon effect asymmetries. However, whereas the first model showed a reversed pattern of asymmetry compared with human, real data, the second model's performance strongly resembled human Simon effect asymmetries, with a significantly greater right than left Simon effect. Thus, a left-side bias in the response-selection mechanism produced a left-side biased Simon effect, whereas a right-side bias in the attention system produced a right-side biased Simon effect. In conclusion, results showed that the bias of the attention system had a larger impact than the bias of the response-selection mechanism in producing Simon effect asymmetries.

Interference between nonspatial stimulus features in the Simon effect.

We investigated whether learning effects influencing the Simon effect, such as those found when learning involves the spatial stimulus dimension, might be also found when learning tasks involve other nonspatial stimulus features, such as color, shape, and orientation. Experiment 1 focused on mutual influences between Simon tasks based on color and shape. The Simon task on color is affected by a previously performed Simon task on shape more than the latter is affected by a previously performed Simon task on color. We hypothesized that this difference depends on the difficulty of the tasks. Because orientation discrimination seems more difficult than both color and shape discrimination (Experiment 2), we predicted that a Simon task on orientation would be influenced by a Simon task on color or shape more than tasks on color or shape would be influenced by a task on orientation. Experiments 3 and 4 confirmed our hypothesis.

Decay of stimulus spatial code in horizontal and vertical Simon tasks.

Evidence on the processes underlying the horizontal and vertical Simon effect is still controversial. The present study uses experimental manipulations to selectively delay the stages of response execution, response selection, and stimulus identification in three experiments. A reduction is observed for both horizontal and vertical Simon effects when response execution is delayed by a go-signal presented 400-600 ms post-stimulus onset or when a spatial precue is presented 200-400 ms before the stimulus. When the overlap between stimulus spatial code formation and response selection is prevented by decreasing stimulus discriminability, the horizontal Simon effect decays, but the vertical Simon effect does not change. Activation theories, which propose a decay of the automatically activated response ipsilateral to the stimulus, mainly apply to the horizontal Simon effect. In contrast, translation theories, which propose that the effect occurs when stimulus features are translated into a response code, are more suitable to account for the vertical Simon effect.

Visuospatial priming of the mental number line.

It has been argued that numbers are spatially organized along a "mental number line" that facilitates left-hand responses to small numbers, and right-hand responses to large numbers. We hypothesized that whenever the representations of visual and numerical space are concurrently activated, interactions can occur between them, before response selection. A spatial prime is processed faster than a numerical target, and consistent with our hypothesis, we found that such a spatial prime affects non-spatial, verbal responses more when the prime follows a numerical target (backward priming) then when it precedes it (forward priming). This finding emerged both in a number-comparison and a parity judgment task, and cannot be ascribed to a "Spatial-Numerical Association of Response Codes" (SNARC). Contrary to some earlier claims, we therefore conclude that visuospatial-numerical interactions do occur, even before response selection.

Lost in number space after right brain damage: a neural signature of representational neglect.

The human brain represents numbers along a mental number line, whose spatial nature was confirmed by studies of patients with visuospatial neglect. Here we describe a neural signature of neglect for the left "number space" by using a task that does not require manipulation of numbers. Patients were asked to discriminate an infrequent ("one" or "nine") from a frequent spoken number word ("five"). P3b brain waves, elicited by infrequent stimuli and indexing cognitive processing, were delayed to targets on the left of the number line ("one") compared to targets on the right ("nine"). The delay of P3b is thus a neural signature of the disorder of representational space.

Spatial coding of word-initial letters: evidence from a Simon-like task.

In this study, we investigated whether the processing of written words leads to a preferential coding of word beginnings and whether this coding occurs in the context of word representations that are spatial in nature and depend on the orientation of the actual stimuli. Two experiments were carried out wherein participants were asked to press a left or right key, in accordance with a nonspatial feature of standard-oriented or mirror-reversed wordlike stimuli (words and pronounceable nonwords). Both experiments showed an effect of correspondence between position of the beginning part of the stimuli and position of the required response (i.e., a Simon-like effect): Responses to standard-oriented stimuli were faster with the left key, whereas responses to mirror-reversed stimuli were faster with the right key. The present findings indicate for the first time that, in reading, the direction of script is automatically processed and the position of the word beginning is coded before the orthographic lexicon is accessed.