Present Study Investigated

Abstract

The present study investigated if the hands have a specialist status in visual attention, then it is expected the hands effect to be more significant with the dominant hand, as the hands effect is due to motor not vision. Participants were asked to carry out a close replication of the Abrams et al (2008) visual search task whilst manipulating the hand adjacent to the stimuli. A 2*2 mixed ANOVA revealed the results did not support the hypothesis that the hands effect is due to action and was concluded a null effect was found.

Introduction

According to psychologist and philosopher William James, attention "is the taking possession by the mind, in clear and vivid form, of one out of what may seem several simultaneously possible objects or trains of thought. …It implies withdrawal from some stimuli in order to deal effectively with others". (The Principles of Psychology,1890). Sensory processing is affected by both endogenous and exogenous mechanisms of attention. Hopfinger and West (2006), investigated how the mechanisms of attention worked in order to understand how multiple stages of information processing in the brain are affected when endogenous and exogenous information is within the visual field. The results provide support for theories suggesting that endogenous and exogenous mechanisms represent two separate attention systems that can affect information processing in the brain.

The past decade Cognitive Psychologist’s have revealed that one’s own hands can bias attention, as they have a special status in visual attention. Abrams, Davoli, Du, Knapp and Paull (2008) carried out a series of visual search experiments during which participants either held their hands near the stimulus (object-proximal posture) or away from the stimulus (object-distal posture), to explore if hand position affected visual processing. When participants had their hands near the stimulus display their visual search efficiency was slower, suggesting that the hands bias attention away from the stimuli. Similarly, Davoli, Du, Montana, Garverick, and Abrams (2010) asked participants to either put their hands near the visual display or far away, whilst they performed semantic processing tasks. One of the tasks was the Stroop colour-word interference task, of which they found the Stroop Effect was reduced when the hands were near the visual display. The results showed a reduced strength of semantic processing in all tasks when the hands were near the visual display. Researchers concluded, again, that the hands took attention away from the distracting word. As recent investigations supported the specialist status of hands due to enhanced processing of information, Davoli and Brockmole, (2012) investigated whether the hands could act as a shield for unwanted interference within the visual attentional window. Participants performed a flanker task, in which they had to identify a target letter within a group of flanking letters, of which varied in the degree of similarity to the target letter. Throughout the study, participants either had their hands around the target so the flanking letters were outside their hands, or their hands were held away from the visual display. Remarkably, the flanking interference was reduced when the hands were around the target letter as the hands were effectively shielding attention from visual interference.

Cognitive Psychology has flourished with studies that demonstrate that the hands can modulate visual attention, however in the past 2 years there has been consideration that possibly this is an effect of action with other body parts, not specifically hands. Previous unpublished data in 2016 replicated the visual search experiment to find the hands effect, but also asked participants to carry out the study with their feet next to the stimuli. The visual search efficiency index revealed that irrespective of what limb is near the stimuli, having a limb near the visual display made participants slower at finding the stimuli. It was concluded that the hands effect was actually a body part effect as participants attended to both the hands and feet, which reduced their speed at finding the visual stimulus. The theory that the hands have a special status to bias visual attention is based upon the primary role hands have in performing motor actions on the world. It can be said that if the hands have a primary role in acting upon the world, then the hands effect would be expected to only occur if the hands are adjacent to the stimuli, as opposed to the hands being far reaching to the stimuli. Essentially, is the hands effect an effect of vision or action? Previous unpublished data in 2017 got participants to do the visual search experiment with their hands either adjacent to the visual display, or their hands up reaching towards the visual display. They found a significant interaction, whereby participants visual search efficiency index was slower when the hands were adjacent to the stimuli compared to their hands reaching towards the stimuli. The data shows that the hands effect is not due to the visual system, but rather the motor system – there would be activity in the frontal lobes, rather than the primary visual cortex.

Therefore, the present study investigated the premise of if the hands have a specialist status in visual attention as they represent the primary way we perform motor actions. It is expected the hands effect to be more significant with the dominant hand, as the hands effect is due to motor not vision. For instance, the hands effect will be larger when a right hand dominant individual has their right hand next to the stimuli, compared with their left hand. Using a 2*2 mixed design, the first factor manipulated had had two levels of handedness: left dominant or right dominant. The second factor manipulated had two levels of which hand was adjacent to stimuli; left hand or right hand. The dependent variable was reaction time of visual search, which then generated the search efficiency index. This was calculated using formula: difference in MS for search time for an 8-item display and 4-item display, divided by the difference in the two set sizes. The data reveals the speed at which attention moves from one stimuli to another. In order to determine which participants were right and left hand dominant, the Edinburgh Handedness Inventory was used. Then participants were put in either the left hand dominant group or right hand dominant group. The study involved participants performing a close replication of the Abrams et al (2008) visual search experiment, which asked participants to search for a target item, either ‘S’ or ‘H’, amongst distractors of ‘E’ and ‘U’. The trials varied from having different set size and it was manipulated to have 4 or 8 items on the visual display. This meant a visual search efficiency index could be calculated. The data was interpreted so that the smaller the visual search index indicated a faster search of the stimuli.

Methods

Participants

An opportunity sample recruited 67 male and female participants, however 3 were omitted as 20% of vocal responses were not registered by the software. 4.2% of responses were outliers and also were not included. This means 64 participants were used in the study.

Design

A 2*2 mixed ANOVA design was used. The first between subjects factor manipulated handedness, the levels were either left dominant or right dominant. The second within subjects factor manipulated was hand adjacent to stimuli (the hand that was placed next to the stimuli), the levels were left hand and right hand.

Materials

The study was run on an iMac OS Sierra (21.5 inch, late 2013) LCD monitor, in a well-lit quiet room. The display showed either 4 or 8 black letters against a white background. The target letters were ‘S’ and ‘H’, and ‘U’ and ‘E’ were distracters. The letters displayed measured approximately 3.8cm in height when viewed from 40cm away from display. The black measured 0.3 cd/m2 and the white measured 84.2 cd/m2. The software ‘Audacity’ recorded vocal responses.

Procedure

Participants had to vocally state whether there was an ‘S’ or an ‘H’ on the display for each trial. The beginning of the trial was initiated by the participants’ response on the previous trial. 128 trials were presented in 2 blocks, so 256 trials in total. The blocks were presented in a counterbalanced order.

Results

In the present study a visual search index was computed using the raw scores from participants performance in the visual search task. The visual search efficiency measured the speed at which participants moved from each stimuli. The data was interpreted so that the smaller the visual search index indicated a faster search of the stimuli. This was needed in order to analyse all the data and carry out the 2*2 factorial ANOVA.

A 2*2 factorial ANOVA revealed the Main Effect of Hand used F(1,62)=0.4, p=0.53, partial eta squared=0.007. The main effect of hand used was non-significant, and there was no effect found. Reaction time was no different when the left or right hand was placed next to the monitor.

A 2*2 factorial ANOVA Main Effect of Handedness F(1,62)=0.017,p=0.9, partial eta squared=0. The main effect of handedness is also non-significant. The reaction times were no different for left or right hand dominant participants.

The hand used and handedness interaction was also non-significant F(1,62)=0.25, p=0.62, partial eta squared =0.004

Figure 1-Showing Search Efficiency Index for handedness and hand used interaction

Discussion

Over the past 10 years, researchers have discovered and produced robust scientific evidence for the connection between one’s visual attention and their hands. When the hands are closely involved, people search through stimuli slower, and take longer to switch between stimuli due to the hands special status in visual attention. The prioritisation of stimuli near the hands is known as the prioritisation effect and when visual search is slower, due to the hands being near to the stimuli, it is known as the disengagement effect. There is now compelling evidence that how people perceive, think about, attend to, and remember visual information depends on how close they have their hands to that information. The present study aimed to investigate if the hands effect was more specifically due to action, rather than one’s vision. The hands represent the primary way in which we perform motor actions upon the world, whereby if the action upon the world theory is true we should expect to see the hands effect to be larger with the dominant hand near the stimuli, compared to the less dominant hand. The results did not support the hypothesis that the hands effect is due to action and was concluded a null effect was found.

The strict prediction of hands having a specialist status within motor actions was found not to be true which challenges many theorists and research within the field of Cognitive Psychology. Yet, in everyday life it is seen that the hands are within the target of the visual stimuli. For instance, someone asking to look at an object will assume they are also allowed to hold the object in their hands, as well as visually looking at it. The interaction of the hands and action is demonstrated all the time, although the present theory challenges this.

Davoli and Brockmole (2012) were able to show the role of the hands and action. The hands were able to shield attention from distractors that were outside the palm area of the hand, yet the effect was not shown with the backs of the hands. This was concluded to be due to the backs of the hands being less functional that the palms and so less represented within the cortex. These findings are not supported by the present study as Davoli and Brockmole (2012) were able to clearly demonstrate the hands are able to distract attention away from other stimuli due to their functional importance in action upon the world. Yet the theory of the hands effect being specifically due to action, rather than one’s vision was found non-significant in the theory tested.

Additionally, unpublished data (2016) results revealed that having a limb near the visual stimuli produced the disengagement effect which meant participants visual search efficiency became slower in the presence of feet and hands. The presence of a hand distracting visual attention is plausible when we consider their functional importance in action upon the world. Yet it could be argued that the feet do not have the same functional importance in action. Similarly, to Davoli and Brockmole’s (2012) conclusions that the backs of the hands are not able to shield attention due to them being less functional than the palms. The feet have less of a primary role in acting upon the world and senses, so it is reasonable to deduce they should not be able to shield attention from distractors due to a reduced functionality. However, the results from the unpublished data in 2016 challenge this. The findings support the present studies results that the hands effect is not specifically due to action as the feet were able to reduce visual search efficiency and produce the disengagement effect, even though the feet do not have a primary role in action. This is supporting that regardless of whether the body part has importance in action or not, it is able to distract attention. Therefore, although the results did not support the hypothesis that the hands effect is due to action and not vision and was concluded a null effect, there are findings which make it understandable to see this null effect.

The present study highlights the impact one’s hands have on visual processing and attention and the necessity to consider more factors that may contribute to the effects hands have on visual attention in future research. Given that previous research has not investigated the premise of the hands having specialist status in visual attention and the theory that the dominant hand should produce the hands effect more so than the non-dominant hand until now, the present study may want to be replicated or built upon in the future. A recommendation for future research is increase sample size in order to benefit from discreet left hand and right hand categories. The Edinburgh Handedness Inventory uses degree to determine whether you are either left or right hand dominant. This means having more participants will make the categories discreet by having extremes. Instead of having participants being ‘mostly right handed’ they will be ‘dominantly right handed’.

Additionally, it would be useful to know the number of participants that will be sufficient enough to support a null hypothesis. In future, research an estimate of the effect size is useful to calculate the number of participants needed in order to avoid Type II error, which is concluding there is no effect when an effect does actually exist. The importance of effect size should be encouraged in future research as it reveals the magnitude of differences found, whereas statistical significance (P-Value 0.05) shows if the findings are likely to be due to chance (Sullivan & Feinn, 2012).

The present study has shown that the hands effect is not due to motor as the dominant hand was found to be non-significant in a close replication of the Abrams et al (2008) visual search experiment. It proposes questions and challenges of past research and new research which potentially could change how people visually consume presented information.