Marc Grosjean

Fitts's Law Holds for Action Perception:

Fittss law is one of the most well-established principles in psychology. It captures the relation between speed and accuracy in performed and imagined movements. The aim of this study was to determine whether this law also holds during the perception of other peoples actions. Subjects were shown apparent motion displays of a person moving his arm between two identical targets. Target width, the separation between targets, and movement speed were varied. Subjects reported whether the person could move at the perceived speed without missing the targets. The movement times reported as being just possible were exactly those predicted by Fittss law (r2 = .96). A subsequent experiment demonstrated the same lawful relation for the perception of a robot arm (r2 = .93). To our knowledge, this makes Fittss law the first motor principle that holds in imagery and the perception of biological and nonbiological agents.

Visuo-spatial processing and the N1 component of the ERP

Asymmetries in posterior ERP components, such as the N1, are generally taken to reflect the visual processing of spatial information in absolute (fixation-based) coordinates. Yet, it is also well established that the position of an object can be coded relative to the position of other objects. To examine the ERP correlates of relative spatial coding, two experiments were conducted in which spatially neutral target stimuli were preceded, accompanied, or followed by laterally presented, task-irrelevant accessory stimuli. Targets presented simultaneously with a lateral accessory evoked, despite physical asymmetry, a bilateral, symmetric N1. Targets that followed the accessory evoked, despite physical symmetry, an asymmetric N1, with a maximum contralateral to the accessory N1. Thus, lateralizations in the N1 range already reflect relative spatial coding rather than just the processing of the absolute location of incoming information.

Seeing while moving: measuring the online influence of action on perception.

The online influence of movement production on motion perception was investigated. Participants were asked to move one of their hands in a certain direction while monitoring an independent stimulus motion. The stimulus motion unpredictably deviated in a direction that was either compatible or incompatible with the concurrent movement. Participants’ task was to make a speeded response as soon as they detected the deviation. A reversed compatibility effect was obtained: Reaction times were slower under compatible conditions—that is, when motion deviations and movements went in the same direction. This reversal of a commonly observed facilitatory effect can be attributed to the concurrent nature of the perception–action task and to the fact that what was produced was functionally unrelated to what was perceived. Moreover, by employing an online measure, it was possible to minimize the contribution of short-term memory processes, which has potentially confounded the interpretation of related effects.

The role of motor simulation in action perception: a neuropsychological case study

Research on embodied cognition stresses that bodily and motor processes constrain how we perceive others. Regarding action perception the most prominent hypothesis is that observed actions are matched to the observer’s own motor representations. Previous findings demonstrate that the motor laws that constrain one’s performance also constrain one’s perception of others’ actions. The present neuropsychological case study asked whether neurological impairments affect a person’s performance and action perception in the same way. The results showed that patient DS, who suffers from a frontal brain lesion, not only ignored target size when performing movements but also when asked to judge whether others can perform the same movements. In other words DS showed the same violation of Fitts’s law when performing and observing actions. These results further support the assumption of close perception action links and the assumption that these links recruit predictive mechanisms residing in the motor system.

The lateralized readiness potential and response kinetics in response-time tasks

Previous studies have found that the magnitude of the lateralized readiness potential (LRP) at the time of response initiation is constant across spontaneous variations in response time in both cued and uncued, speeded tasks. Other studies have found that the LRP is also unaffected by instructed changes in peak response force and time to peak force in cued, self-paced tasks, but that the LRP is sensitive to instructed changes in force gain rate in uncued, self-paced tasks. The present study examined the LRP in an uncued, speeded task as a function of response time and several measures of response kinetics. The magnitude of the LRP at the time of electromyographic onset was constant across spontaneous variations in all measures. The peak of the contingent negative variation did vary as a function of peak response force and integrated force to peak, but not response time. These findings support the idea that the LRP in speeded tasks is a selective, on-line index of the preparation associated with using a particular hand, and is not an index of the elements of motor programming that determine subsequent response kinetics.

Using inattentional blindness as an operational definition of unattended: The case of surface completion

Studying inattentional processing is made difficult by the fact that measuring it often results in observers attending to the stimuli in question. Here it is suggested that inattentional blindness—the lack of awareness of stimuli that appear in unattended regions of the visual field—be used as an operational definition of unattended. Separate online measures, taken while the stimuli are still present, can then be used to probe specific aspects of processing. Applying this method to the perceptual completion of partial surfaces, an online measure of modal and amodal completion was developed, and then used within an experiment in which inattentional blindness to the surfaces was assessed. The results indicated that surface completion can be engaged by unattended stimuli. More generally, the study illustrates the usefulness of this approach for probing what processing does and does not occur for stimuli that appear in unattended regions of the visual field.

Temporal Stimulus-Response Compatibility

The study of element-level stimulus-response compatibility (SRC) has predominantly focused on spatial and symbolic relationships and has involved measures of response time and (dichotomous) error rate. This article explores a new form of SRC that is observed when duration is the relevant feature of both the stimulus and the response, using a more extensive analysis of performance accuracy and variability. The results indicate that element-level SRC generalizes to situations involving time as the relevant dimension of stimuli and responses. Evidence of this was found in all of the extracted measures of performance; however, temporal SRC was shown to have independent effects on when and how accurately a response was made. Implications for SRC research are discussed.

Using inattentional blindness as an operational definition of unattended: The case of a response-end effect

Inattentional blindness (IB), which is the lack of awareness of stimuli that appear in unattended regions of the visual field, can be used as an operational definition of unattended. Using separate online measures in combination with IB can be used to probe specific aspects of processing that are engaged by unattended stimuli. Previous applications of this method have provided evidence that unattended stimuli can engage processes that lead to grouping‐by‐similarity (Moore & Egeth, 1997), as well as processes involved in the perceptual completion of partially visible surfaces (Moore, Grosjean, & Lleras, 2003). Here we applied this method to address the question of whether unattended stimuli can engage response–end processes. Specifically, we used a stimulus–response compatibility effect, the Simon effect (e.g., Simon & Rudell, 1967), as an online measure of response selection. As assessed through this measure, unattended stimuli failed to engage response‐selection processes.

Post-response stimulation and the Simon effect: Further evidence of action-effect integration

The recently proposed action-concept view of perceptual-motor behaviour posits that a stimulus which consistently follows a certain response will become associated with that response. Some evidence in favour of this view comes from the finding that the size of the Simon effect can be altered by the inclusion of post-response stimuli. However, only one study has investigated the effects of including same-side in addition to opposite-side post-response stimuli, as well as a neutral Simon condition, and, possibly because of a failure of random assignment, the results from that study were inconclusive. In light of this limitation, a Simon experiment was performed in which the location of post-response stimulation was manipulated within subjects. The results showed that: (1) the Simon effect can both decrease and increase in the presence of post-response stimuli, and (2) the amounts of Simon interference and Simon facilitation are both affected by post-response stimuli, whereas performance on neutral trials is not. These findings provide additional support for the action-concept view and suggest that further research concerning this new approach is warranted.

A contrast effect between the concurrent production and perception of movement directions

With three experiments, we explored the nature of specific interference between the concurrent production and perception of movements. Participants were asked to move one of their hands in a certain direction while simultaneously trying to identify the direction of an independent and non-biological stimulus motion. Perceived direction of the stimulus was assessed with either above/below judgements (Experiment 1), same/different judgements (Experiment 2), or the adjustment of a line (Experiment 3). The results revealed a form of contrast effect: Perceived directions were repulsed by produced directions. Moreover, the size of the effect was comparable across the three experiments, which points to its robustness and allowed us to control for potential confounds associated with some of the perceptual measures. These results alleviate concerns regarding the interpretation of related findings and demonstrate that effects of this type are not tied to the processing of biological motion, as previously proposed.