Nicola Jane Hodges

How we learn from observing others perform reaching tasks is debated in the adaptation literature. When observers see a hand intentionally miss a target to correctly counteract rotated visual feedback (adaptation error), after-effects are typically absent. In contrast, observing consistent target errors, has resulted in unintended compensatory after-effects. The type of observed “error” (adaptation versus target error) may therefore have different effects on observation-induced behaviour, although this has not been tested within the same experiment. We compared participants in a four-group orthogonal design, who saw a model hit or miss a target, with or without rotated cursor feedback. Small compensatory after-effects (pre- to post-test) were seen when reaching to perceived midline in groups that observed target errors (misses). However, there were also small imitative after-effects after observing adaptation errors without target errors, but only when reaching to visual targets. Observing adaptation errors with or without target misses aided later performance in the same rotated environment and was accompanied by explicit knowledge of the rotation. Knowing the task goal is relevant information for eliciting small compensatory aiming biases in observers, perhaps because target errors matter more than adaptation errors when observing, leading to an unintended resolution not needed for “correct” actions.

There has been considerable interest in the relatively newly identified inability of some people to visually imagine, termed aphantasia. Aphantasia is argued to be qualitatively different to hypophantasia, which is a poor ability to visually image and thus comprises distinct characteristics. Whilst, by definition, aphantasia is the absence of visual imagery, there are debates about the consequences of aphantasia for other imagery modalities, including motor imagery (MI). We conducted an online survey of people who self-reported as having aphantasia (N = 172). Participants completed three validated measures of imagery ability; the Vividness of Visual Imagery Questionnaire (VVIQ), the Movement Imagery Questionnaire-3 and the Plymouth Sensory Imagery Questionnaire. Means were low for all measures, with the sample averaging 22 on the VVIQ (range 16-80). However, there was high variation. When the individual items from these measures were entered into an exploratory factor analysis, four factors were identified. Notably, visual imagery was related to visual-MI from an external perspective, but not internal MI (neither visual or kinesthetic). As such, although aphantasia impacts all types of imagery, including MI, non-movement visual imagery is a distinct feature of aphantasia. Kinesthetic MI grouped with body sensations and emotional imagery and a final multisensory factor emerged (taste, smell, sound, sensation, touch). We also accessed task-specific kinesthetic MI (two ball juggling). Experience with the task did not impact imagery quality. These results show the heterogenous nature of aphantasia, with the factors informing potential subtypes of aphantasia, aiding research and potential design of aphantasia-specific measures.

The human sensorimotor system can represent actions in the absence of movement, termed motor simulation. These motor simulations can be perceptually (externally) driven through observation of an actor or cognitively (internally) driven through imagining movement. Although there is evidence humans can represent multiple actions simultaneously, whether different motor simulations can concurrently be represented is unclear. We investigated the capacity of the sensorimotor system to simultaneously represent observed (action observation; AO) and imagined actions (motor imagery; MI). Two competing hypotheses were tested concerning whether AO and MI could co-exist or not, The Dual Action Simulation Hypothesis (DASH) and Visual Guidance Hypothesis (VGH), respectively. Fifteen participants completed a functional magnetic resonance imagining (fMRI) study, requiring them to complete four distinct conditions involving imagination or observation of a rhythmical hand tapping action. Conditions involved; AO, AO with a counting task (i.e., with cognitive load), MI, or simultaneous AO and MI of different actions (AOMI). Through representational similarity analysis, AO and MI motor simulations were evidenced within the ventral premotor cortex and to an extent the inferior parietal lobule, supporting DASH over VGH. Multidimensional scaling of representational similarity data indicated a unique representational pattern for AOMI, differing with AO and MI across different dimensions. Whole-brain analyses revealed greater engagement of sensorimotor regions during AOMI than the summation of the independent AO and MI conditions. While dual motor simulations appear possible, our data suggests the representational pattern of AOMI is distinct and produces super-additive sensorimotor activity, of which DASH and VGH do not account for.

Physical and observational practice of multiple skills in a random versus blocked order brings beneficial “interference” into practice, aiding later retention (contextual interference effect). Little is known about the moderating effects of a partner on the learning of multiple skills, especially when partners take turns practicing the same (matched) or different (mismatched) skills. Here, we used a timing task to determine whether variation in a partner’s practice augments learning for the partner. Four groups completed blocked practice of three different sequences either alone ( n = 34) or in pairs ( n = 98). Their partners did matched- or mismatched-blocked or random practice (16–17 pairs/group). In acquisition, the alone group had the highest error, despite having the lowest between-partner variability. However, in retention, there was evidence of partner-induced contextual interference effects. Mismatched dyads, irrespective of whether variability was physically or vicariously experienced, were generally more accurate in retention than matched dyads and the alone group. These data show that dyad practice provides a means for bringing contextual interference into practice to aid learning, without costs in acquisition. We conclude that observing and practicing in a turn-taking manner affords learning benefits associated with more distinct action representations, especially when partner’s actions are mismatched.

Research investigating the behavioral and psychosocial outcomes of individuals practicing motor skills in pairs (dyad practice) has generated mixed evidence regarding its effectiveness when compared with individuals practicing alone. The purpose of the present study was to investigate the motor performance, learning, and psychosocial outcomes associated with competitive or cooperative dyad practice contexts versus practicing alone. Participants practiced a relative-timing keypress sequence task alone, or in competitive or cooperative dyads. Relative timing errors for each movement component in the sequence were measured across the 40 practice trials and in a 24-hr retention test. Psychosocial measures of positive and negative affect, motivation, and efficacy were also collected. There were no group differences in timing errors during practice or retention, although partners in the cooperative group were more alike (correlated) in performance compared with partners in the competitive group. The cooperative group also reported higher levels of interest/enjoyment and commitment to continue practicing compared with the competitive group, but these outcomes were not different from the alone group. Overall, although there were indications that cooperative dyad practice led to greater task engagement and task “sharing” than competitive dyad practice, these effects did not impact the acquisition and retention of the motor skill.

We investigated how separately and sequentially acquired visual and motor experiences shape action prediction mechanisms. There is evidence that physical practice leads to an implicit, motor-based prediction process, compared to visual practice, which is more strategic. However, the relative dominance or flexibility of these mechanisms is not well understood. Here we used a motor secondary task paradigm to evaluate effector-specific interference in action predictions, which has previously given evidence for a motor simulation-based prediction process after physical practice. Participants across two groups (N = 40) received both isolated and sequentially combined motor and visual practice across two days; either throwing darts to three different sections of a dartboard “motor” or watching and predicting outcomes of occluded throws “visual”. The Motor-to-Visual group threw on Day 1 and watched on Day 2 and the Visual-to-Motor group did the reverse. Prediction tasks were performed pre and post practice each day, with some trials involving motor secondary tasks, performed with the observed (right) or non-observed hand. Consistent with previous work, the Motor-to-Visual group after physical practice improved prediction accuracy on Day 1, except when performing the secondary task with their right hand. After visual practice on Day 2, prediction accuracy was maintained, but without secondary task interference. The Visual-to-Motor group also improved predictions, but with no secondary task interference on either day, resulting in greater accuracy overall. These data support the suggestion that separately acquired motor and visual experiences either allow flexibility in prediction strategies or lead to a dominance of the visually-acquired strategy.

Watching others act can cause unintentional biases in the observer’s next action. This “contagion” occurs due to the shared processes engaged during observation and execution, interfering with performance after observation. Biases can be imitative or compensatory, with the direction thought to be dependent on the presence of observed-induced prediction errors (PE: difference between predicted/expected and observed performance). To replicate and test the proposed PE mechanism, we compared golfers watching “on-target” and errorful putts. Twenty-three experienced golfers alternated putting a ball to a centre target on a nine-square grid (without outcome feedback) and watching videos of an actor putting to the same grid. Across four conditions, we covaried the location of the actor’s putts (centre, corner) and expectations about the actor’s aiming location, to manipulate the presence of a PE. As expected, imitative execution biases emerged after watching “correct” putts to corner squares, but not when these same corner putts were perceived as errors. Compensatory biases from PEs were also absent after watching “misses” to the centre square. These data provide evidence for different behaviours after the observation of correct versus errorful actions but raise questions about the types and/or stability of errors that underpin these effects.

Both visual and motor experiences impact action prediction, yet through potentially different mechanisms. Having physical experience with an action is thought to engage motor simulative processes, potentially activating the watcher’s motor system in an effector-specific manner, aiding prediction. Leveraging baseball’s unique specialization demands, we assessed pitch discrimination in athletes with predominantly visual experience seeing pitches (hitters, n = 41; 7 = left-handed hitters) and motor experience producing pitches (pitchers, n = 42; 9 = left-handed). Videos of right-handed (RH) pitches, with temporal occlusion applied at or after ball release, of three different pitches, were used to assess pitch prediction accuracy. Two versions of each video clip were shown; the original RH clips were “flipped” to make the pitcher appear to throw left-handed (LH). Pitchers and hitters had reliable responses and showed high accuracy (~70%) and discriminability. Pitchers were more discriminatory than hitters when contrasting two pitch types with the same initial trajectory and speed, but different postural cues (curveballs and changeups; d’ pitchers = 2.18, hitters = 1.88). Although there was the predicted interaction for the pitchers when comparing LH and RH pitchers watching LH and RH videos (p<.05), only LH pitchers showed a trend for a same-side, LH video advantage (p=.06). Because pitchers did not differ in accuracy from hitters, despite a lack of visual experience seeing and responding, this suggests that their motor experience aided predictions. However, there was only partial support for a simulation explanation based on effector specificity (due to absence of any differences in RH pitchers).