Abstract
The phenomenon of apparent motion occurs when two stimuli are separated by a flash or a blank in which the brain creates the effect of movement. It can be compared to the effects of moving pictures, for example, in which a series of still photographs are put together in such a way that the image appears to be moving. The purpose of this research is to assess the phenomenon of apparent motion in terms of the interstimulus interval, the gap between two stimuli that most accurately conveys movement to the perceiver. The study used five different dot spacings, and participants were asked to adjust the ISI until they felt that the perception of movement was strongest to them. No statistically significant difference was found concerning the spacing of these dots and the ISI, suggesting that the actual distance between two stimuli is not a factor in determining the ISI and the perception of movement.
Apparent motion is a concept in psychology that describes the phenomenon of how a stimulus appears to move when it is separated from a later stimulus by a brief flash. The effect of this illusion can be seen in movies, for example, when a number of static images are strung together in such a way that the characters appear to be moving. It is also important that the gap between the two stimuli is long enough to account for the motion that should be portrayed – the separation flash should be longer if the appearance of motion needs to be further, whereas a brief flash is all that is needed to separate small movements. The purpose of this research is to assess the interstimulus interval (ISI) that best represents movement in the case of two dots presented to participants. This will give insight into how the phenomenon works in terms of timing and vision.
A number of different research projects have been conducted on the phenomenon of apparent motion. Wibral, Bledowski, Kohler, Singer & Muckli (2008) found that there is measurable brain activity that is associated with processing visual stimuli. The phenomenon is associated with feedback moving from the human motion complex hMT/v5 to V1, showing that the perception of movement between stimuli is found directly in the cerebral cortex. Ahmed et al. (2008) also investigated the biopsychological aspect of apparent motion, finding that perception of visual stimuli can be mapped to areas 17 and 18 when they are seen as stationary, but the phenomenon of apparent motion occurs when there is an activation of neurons between area 17/18 and area 19/21. Again, this highlights the area of apparent motion in the brain.
Several studies have investigated the effect of certain mental illnesses on the perception of apparent motion. This is important as it can give insight into how normal processes are affected by mental illness, and give insight into both mental health and the function of the process as part of a healthy brain. Chen (2011) found that there are a number of motion perception issues found in patients with schizophrenia. In these cases, there is an imbalanced regulation of the spatial interaction processes when an individual has schizophrenia, meaning that they are unable to perceive apparent motion. It is interesting to consider the relationship between schizophrenia and apparent motion, as it could be that this difference between schizophrenic and non-schizophrenic individuals can be used as an early diagnostic technique for the disease.
Several pieces of research have also investigated the impact of auditory stimuli on visual apparent motion. Freeman & Driver (2008) found that the direction of apparent motion can be changed based on the presence of a static sound, used at a specific time. This suggests that there are many different pathways associated with visual motion, and that these can be triggered in different ways to change the perception of the stimuli. Getzmann (2007) also found that there was a strong effect of auditory stimuli on visual apparent motion. In this study, both relevant and irrelevant sounds were found to have an effect on the visualization of apparent motion. This gives insight into the way that apparent motion works as a psychological phenomenon, and the way that it can be manipulated by external environments. In this report, the focus is on how the distance between stimuli has an effect on the time spacing needed to convey motion. This will add to the previous body of research on the different elements that make up the phenomenon of visual apparent motion.
Methods
The aim of this research is to assess the correlation between dot spacing (visual stimuli) and the ISI time in terms of apparent motion. This section describes the participants, materials, and procedure that was used to conduct the current research and assess this phenomenon. A simple computer program was used in order to provide five different scenarios in which the participants were asked to make judgments about ISIs in terms of stimulus motion percepton.
Participants
The participants for this project were 140 undergraduate students. All participants took part in all conditions. The participants were sampled through word-of-mouth, and agreed to take part in the research. All gave fully informed consent about taking part in the research and for their results to be used as part of this report. No demographic information was collected about the participants as part of this research, as the key variable of interest is how the difference between dots affects the ISI, rather than specifically into how demographic variables affect personal perception of apparent motion.
Materials
The premise of this research is based around the assessment of the phenomenon of apparent motion. One of the easiest ways of assessing this is to use ready-made software that is designed to allow participants to extend or shorten the time between stimuli in order to recreate the phenomenon accurately from their own perspective. As such, the materials for this study include a computer that is running the program that allows participants to complete this process. The participants were also given the option of completing the research on a handheld tablet.
Procedure
The participants were each given access to a computer running the program required for this investigation. They were given basic information about the study, and then asked if they understood the procedure and agreed to take part. They were then asked to log in, and ensure that they could see the entire screen before starting the lab procedure.
Each trial showed a dot appearing on the right, followed by disappearance. A dot then appeared on the left of the screen and disappeared. The participants were then asked to assess the ISI to make it look as though these dots were the same dot, moving across the screen. They were informed that the main task is to adjust the ISI until the motion percept is as strong as they could make it.
There were five different dot spacings, each of which were replicated five times, giving a total of 25 trials that were part of this experiment. The spacing of the dots varied between each trial. The trials were presented in a random order to prevent bias.
At the end of the experiment, the participants were asked if they wanted to save data to a set of global data. After this question was answered affirmatively, a new Web page window opened that included a debriefing, individual data, group data, and the global data as relevant to this research project.
Results
A within-subjects one-way ANOVA was used to analyze the data, with the distance between the dots (DbD) as the independent variable and the inter-stimulus interval (ISI) for producing the best illusion of motion as the dependent variable.
The results of the one-way ANOVA revealed no significant effect of distance between the dots, F(4, 560) = 1.92, p = .12 on the ISI for producing the best illusion of motion. Therefore, it appears that distance between the dots does not significantly affect the ISI needed to produce an illusion of apparent motion. The following results were found:
The average best ISI in the DbD_80 condition was 343.15 ms., with a standard deviation of 148.19.
The average best ISI in the DbD_160 condition was 344.65 ms., with a standard deviation of 140.66.
The average best ISI in the DbD_240 condition was 345.08 ms., with a standard deviation of 153.33.
The average best ISI in the DbD_320 condition was 354.30 ms., with a standard deviation of 166.74.
The average best ISI in the DbD_400 condition was 358.04 ms., with a standard deviation of 174.08.
Note: DbD is an abbreviation for distance between dots, ISI is an abbreviation for inter-stimulus interval (the time between the disappearance of the first dot and the appearance of the second dot in milliseconds) and the number next to the DbD is the number of pixels separating the dots.
Discussion
There is no significant difference found between any of the experimental conditions highlighted above. This suggests that, whilst there are increases in the ISI based on the distance between dots, this does not have a strong enough effect to classify as having an impact on the phenomenon. Overall, the assessment can be made that the distance between dots does not have an impact on the ISI needed to give the participant the effect of apparent motion, which means that distance between dots is not a variable in recreating the phenomenon in a laboratory setting.
The results of this study are interesting in the context of previous research on apparent motion. Both Getzmann (2007) and Freeman & Driver (2008) found that audio stimuli had an effect on the perception of apparent motion in their studies. Compared with the results of the current research, this suggests that audio is much more important in determining the perception of motion than the actual distance between dots, as this has an effect on the ISI and distance does not. It would be interesting to conduct further research to make assessments whether the combination of different dot spacing and different auditory stimuli has an effect on ISI or other measurements of apparent motion.
Chen (2011) suggested that those with schizophrenia cannot perceive apparent motion in the same way as healthy individuals. In this context, it would be interesting to compare the results of this study with a similar experiment involving schizophrenic individuals to assess whether this holds true in terms of dot spacing. This would give a deeper insight into the role that dot spacing plays in terms of ISI and the perception of apparent motion.
Overall, this research has added to the general body of literature on apparent motion and the different stimuli effects that can be used to manipulate it in the laboratory setting. Whilst there is no significant difference between each of the conditions, this still allows for insight into how distance affects the perception of motion between two still images. This research can be used as a basis for further research on the topic to assess whether there are other variables that have an effect on ISI, or to assess the effect of combinations of stimuli on the perception of apparent motion in healthy patients. It is hoped that this research will have implications for further study into the pathways of apparent motion that can be used in a wide variety of situations to understand the illusion process in further detail.
Limitations
There are a number of limitations of this study. The main limitation is that the small sample size only included undergraduate students, and therefore the results may not be applicable to the ISIs that simulate motion for the population as a whole (Robson & McCartan, 2016). Another issue is that the participants knew of the nature of the phenomenon before they started the trial, and this could have had an effect on how they perceived the motion of the dot, and the ISI result that they felt was most appropriate. Another limitation is that the conditions were not that varied, and therefore does not give information about the phenomenon of apparent motion in general, rather about the phenomenon of apparent motion as it concerns moving dots on computer or tablet screens. It may be useful to research into various different types of apparent motion to give a larger picture about the phenomenon in general.
Suggestions for Future Research
Future research holds a number of possibilities for further understanding the phenomenon of apparent motion. It would be interesting to assess whether the nature of the visual stimuli has an effect on the ISI required for each of the conditions. A dot may need a shorter or longer ISI than a picture of a dog moving from the left to the right of the screen, for example. This will help highlight the impact of the stimulus itself on apparent motion, and whether there are any reasons why people choose the ISI that seems most appropriate to them.
It would also be interesting to assess whether there are demographic differences in ISI, for example, between male and female participants, or those from different socioeconomic backgrounds. If apparent motion is a psychological phenomenon, rather than a visual phenomenon, this will give insight into whether there is an environmental or biological effect on the ISI perception required to simulate the appearance of motion. This will give further insight into the phenomenon and how it works in terms of individual psychology.
References
Ahmed, B., Hanazawa, A., Undeman, C., Eriksson, D., Valentiniene, S., & Roland, P. E. (2008). Cortical Dynamics Subserving Visual Apparent Motion. Cerebral Cortex, 18(12), 2796–2810. http://doi.org/10.1093/cercor/bhn038
Chen, Y. (2011). Abnormal Visual Motion Processing in Schizophrenia: A Review of Research Progress. Schizophrenia Bulletin, 37(4), 709–715. http://doi.org/10.1093/schbul/sbr020
Freeman, E., & Driver, J. (2008). Direction of visual apparent motion driven solely by timing of a static sound. Current Biology, 18(16), 1262–1266.
Getzmann, S. (2007). The effect of brief auditory stimuli on visual apparent motion. Perception, 36(7), 1089–1103.
Robson, C., & McCartan, K. (2016). Real world research. Wiley. Retrieved from http://eprints.uwe.ac.uk/27650
Wibral, M., Bledowski, C., Kohler, A., Singer, W., & Muckli, L. (2009). The timing of feedback to early visual cortex in the perception of long-range apparent motion. Cerebral Cortex, 19(7), 1567–1582.
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