End-state-comfort effect

These two videos of Rona (4y 9m) and Will (3y 2m) were originally made to illustrate the emergence of planning for end-state-comfort concept. This they do well with Rona showing a transition to end state comfort planning over repeated trials of turning beakers over.  Will on the other hand stays with his preferred action despite twice starting the action with the hands initially positioned to allow for a comfortable end position. 

Turning the beakers over with one hand is a novel experience and requires more attention, ongoing visual monitoring and elicits exploration of different options. When instructed to use only one hand they need to develop a different strategy. Both children manage to turn the beakers over with one hand. Will sticks to using his preferred pattern but Rona starts to explore changing her start position to achieve a comfortable end position. 

Will ending action in an uncomfortable position

W 3y 2m  turning cup one hand.jpg   W 3y 2m  turning cup one hand 1.jpg

Rona adapting initial grasp to end action in a comfortable position

R turning cups one hand 6_1.jpg   R turning cups one hand 7.jpg

Interestingly Will initiates the turning over action with the forearm in pronation to allow for a comfortable end position, but before he grasps the beaker he reverts to grasping with the forearm in a more comfortable mid-range position. 

W 3y 2m  turning cup one hand 4.jpg   W 3y 2m  turning cup one hand 5.jpg

Rona (4y 9m) turning over cups

Notice the difference in visual information pickup

Besides observing Roan's emergent tendency to plan for end state comfort, I was also struck by the different use of visual information pick up between the well practised two handed sequence of movements and the novel one handed action. 

In the two handed action the hands movements are smoothly coordinated in space and time and brief periods of visual fixation on the beaker is all that are needed  to get the needed information about the position of the beaker. On the other hand when using the unpracticed one hand strategy, Roan appears to need online visual guidance for controlling the action. 

Will (3y 2m) turning over beakers 


Bibliography

1: Wilmut K, Byrne M. Influences of grasp selection in typically developing children. Acta Psychol (Amst). 2014 May;148:181-7. 

When reaching towards an object, adults favour grasps which, following the intended action, end in a comfortable position even when this requires them to start in an uncomfortable position (the end-state-comfort effect). However, this strategy is not consistently used by children who instead seem to favour a minimal pre-contact rotation of the hand, even when this results in an uncomfortable end position. In terms of multiple movements, the strategies used for grip selection are unclear; adults may still grasp for end-state-comfort given their propensity to plan to the end of a movement; however, children who are less able to concatenate movement may tend to start-state-comfort movements. The current study considered grip selection in children ranging from 4 to 12 years and in a group of adults. Participants were asked to rotate a disc so that an arrow pointed towards a specific target(s), the number of sequences in a movement was increased from one to three. Planning for end-state-comfort was seen in all participants and a clear developmental trajectory was identified whereby the relative comfort of an end position could be directly predicted by age in months. Adults and 10-12-year-olds favoured an end-state-comfort strategy whereas the younger children gave equal weighting to end-state-comfort, start-state-comfort and no initial rotation strategies. All groups were able to end a movement comfortably when it was composed of three steps; however, the proportion of movements relying on an end-state-comfort strategy decreased as sequence length increase whereas the proportion of start-state-comfort and no initial rotation strategies increased. The current data support the concept that a mechanism for planning grasps may be based on motor experience.

2: Hermens F, Kral D, Rosenbaum DA. Limits of end-state planning. Acta Psychol (Amst). 2014 May;148:148-62. 

The end-state comfort effect is the tendency to use an uncomfortable initial grasp posture for object manipulation if this leads to a comfortable final posture. Many studies have replicated the end-state comfort effect across a range of tasks and conditions. However, these tasks had in common that they involved relatively simple movements, such as picking up a dowel or sliding a pan from one place to another. Here we asked whether the end-state comfort effect extends to more complex tasks. We asked participants to grasp a transparent bowl and move the bowl to an instructed location, positioning it in an instructed orientation. We either found an initial-state comfort effect or equal degrees of comfort for end-grasps and start-grasps depending on task instructions. The end-state comfort effect was not consistently observed. The results suggest that the end-state comfort effect may be restricted to relatively simple grasping movements.

3: Wilmut K, Byrne M. Grip selection for sequential movements in children and adults with and without evelopmental Coordination Disorder. Hum Mov Sci. 2014 Aug;36:272-84. 

When generating a movement adults favor grasps which start the body in an uncomfortable position if they end in a comfortable position (the end-state-comfort effect). In contrast, children with Developmental Coordination Disorder (DCD) select grasps which require little initial hand rotation even though they result in an uncomfortable end position. The current study considered grip selection of individuals with DCD when asked to make simple one step movements and when making more complex multi-staged movements. Adults with DCD (N=17, mean age 24:09, SD age=52months) and children with DCD (N=20, mean age 9:00, SD age=20months) and age and gender matched controls rotated a disc so an arrow pointed toward a specific target(s). Task complexity was increased by increasing the number of targets from 1 to 3. Planning for end-state-comfort was seen in all groups albeit to a lesser extent in children versus adults. The children with DCD showed fewer grips for end-state-comfort compared to their peers and this was explained by a propensity to select minimal initial rotation grasps. This result was mirrored in adults with DCD but only for the longest movement sequence. These results suggest some changes in ability from childhood to adulthood in individuals 

4: Knudsen B, Henning A, Wunsch K, Weigelt M, Aschersleben G. The end-state comfort effect in 3- to 8-year-old children in two object manipulation tasks. Front Psychol. 2012 Oct 29;3:445. 

The aim of the study was to compare 3- to 8-year-old children's propensity to anticipate a comfortable hand posture at the end of a grasping movement (end-state comfort effect) between two different object manipulation tasks, the bar-transport task, and the overturned-glass task. In the bar-transport task, participants were asked to insert a vertically positioned bar into a small opening of a box. In the overturned-glass task, participants were asked to put an overturned-glass right-side-up on a coaster. Half of the participants experienced action effects (lights) as a consequence of their movements (AE groups), while the other half of the participants did not (No-AE groups). While there was no difference between the AE and No-AE groups, end-state comfort performance differed across age as well as between tasks. Results revealed a significant increase in end-state comfort performance in the bar-transport task from 13% in the 3-year-olds to 94% in the 8-year-olds. Interestingly, the number of children grasping the bar according to end-state comfort doubled from 3 to 4 years and from 4 to 5 years of age. In the overturned-glass task an increase in end-state comfort performance from already 63% in the 3-year-olds to 100% in the 8-year-olds was significant as well. When comparing end-state comfort performance across tasks, results showed that 3- and 4-year-old children were better at manipulating the glass as compared to manipulating the bar, most probably, because children are more familiar with manipulating glasses. Together, these results suggest that preschool years are an important period for the development of motor planning in which the familiarity with the object involved in the task plays a significant role in children's ability to plan their movements according to end-state comfort.

5: Jongbloed-Pereboom M, Nijhuis-van der Sanden MW, Saraber-Schiphorst N, Crajé C, Steenbergen B. Anticipatory action planning increases from 3 to 10 years of age in typically developing children. J Exp Child Psychol. 2013
Feb;114(2):295-305. 

he primary aim of this study was to assess the development of action planning in a group of typically developing children aged 3 to 10 years (N=351). The second aim was to assess reliability of the action planning task and to relate the results of the action planning task to results of validated upper limb motor performance tests. Participants performed an action planning task in which they needed to grasp an object (a wooden play sword) and place it into a tight-fitting hole. Our main dependent variable was the grip type that participants used; that is, we measured whether initial grip was adapted in such a way that children reached a comfortable posture at the end of the action (the end-state comfort effect). Older children planned their actions more often in line with the end-state comfort effect compared with younger children. Test-retest and interrater reliability of the action planning task were good, with intraclass correlation coefficients (ICCs) of .90 and .95, respectively. We compared the action planning task with manual dexterity tests in a subset of participants (n=197). We found a marginal relation with the manual dexterity tests, indicating that the action planning task measures different processes. In sum, our study showed that action planning increases from 3 to 10 years of age and that the experimental task we used is reliable in assessing anticipatory planning. Therefore, it may be used as a reliable additional test to investigate the degree to which motor behavior is affected at the cognitive level of anticipatory planning.

6: Hughes CM, Seegelke C, Spiegel MA, Oehmichen C, Hammes J, Schack T. Corrections in grasp posture in response to modifications of action goals. PLoS One. 2012;7(9):e43015. 

There is ample evidence that people plan their movements to ensure comfortable final grasp postures at the end of a movement. The end-state comfort effect has been found to be a robust constraint during unimanual movements, and leads to the inference that goal-postures are represented and planned prior to movement initiation. The purpose of this study was to examine whether individuals make appropriate corrections to ensure comfortable final goal postures when faced with an unexpected change in action goal. Participants reached for a horizontal cylinder and placed the left or right end of the object into the target disk. As soon as the participant began to move, a secondary stimuli was triggered, which indicated whether the intended action goal had changed or not. Confirming previous research, participants selected initial grasp postures that ensured end-state comfort during non-perturbed trials. In addition, participants made appropriate on-line corrections to their reach-to-grasp movements to ensure end-state comfort during perturbed trials. Corrections in grasp posture occurred early or late in the reach-to-grasp phase. The results indicate that individuals plan their movements to afford comfort at the end of the movement, and that grasp posture planning is controlled via both feedforward and feedback mechanisms.

7: Chapman KM, Weiss DJ, Rosenbaum DA. Evolutionary roots of motor planning: the end-state comfort effect in lemurs. J Comp Psychol. 2010 May;124(2):229-32. 

Humans (Homo sapiens) anticipate the consequences of their forthcoming actions. For example, they grasp objects with uncomfortable grasps to afford comfortable end positions-the end-state comfort (ESC) effect. When did such sophisticated motor planning abilities emerge in evolution? We addressed this question by asking whether humans' most distant living primate relatives-lemurs-also exhibit the ESC effect. We presented 6 species of lemurs (Lemur catta, Eulemur mongoz, Eulemur coronatus, Eulemur collaris, Hapalemur griseus, and Varecia rubra) with a food extraction task and measured the grasp used-either a canonical thumb-up posture or a noncanonical thumb-down posture. The lemurs adopted the thumb-down posture when that hand position afforded a thumb-up posture following object transport, thereby exhibiting the ESC effect. We conclude that the planning abilities underlying the ESC effect evolved at least 65 million years ago, or 25 million years earlier than previously supposed based on an earlier demonstration of the ESC effect in cotton-top tamarins (Saguinus oedipus; Weiss, Wark, & Rosenbaum, 2007). Because neither cotton-tops nor lemurs are tool users, the data suggest that the cognitive abilities implicated by the ESC effect are not sufficient, although they may be necessary, for tool use.