Research on the Silencing by Motion Illusion

The silencing by motion illusion (Bach, 2019) is a perceptual phenomenon which consists of a group of varying objects (shape, size, brightness and colours) which move around a central fixation cross, causing the changing properties to be unnoticed by the viewer, while the objects are in motion (Suchow & Alvarez, 2011).

Suchow and Alvarez (2011) proposed implicit updating of memory as a justification for motion silencing. Hollingworth and Henderson (2004) research supports this as it indicated that visual memory would be updated with environmental modification, even without explicit detection. The disparity between the visual memory (initial state of the object) and the actual perceptual information is small. Thus, the change blindness occurs due to the dissociation between visual memory and explicit change processing.

Silencing is also argued to occur due to the motion in the retina i.e. the objects move while the gaze is fixed on them. In order to perceive the modification of a moving object the visual system must record its position into retinotopic maps (each point in the map equates to a position in the visual field). However, the brief exposure of a moving item to the retinotopic receptors might not be sufficient to detect any type of alteration (Suchow & Alvarez,2011). As a solution, attention could be used as a mechanism to combine data from multiple retinotopic points to reduce change blindness (Suchow & Alvarez, 2017).

Additionally, silencing is suggested to be regulated by integration of global motion as well as the crowding mechanism (Turi & Burr 2013). Global motion summates the dynamic shifting signals of the individual dots over large regions (neurons that fire responding to changes in motion, in the medial superior temporal region, have extended receptive fields). Consequently, individual changes are unnoticed. The crowding mechanism merges the dots together, averting the individual changes of the dots to be perceived in the periphery (fovea).

Kavsek (2013) investigated the effect of the silencing illusion in four-month-old infants. The results indicated that motion abolished colour changing perception; this might be because the dorsal processing in the cortical pathway (regulates motion perception) overrules the ventral processing (regulates colour perception). This indicates that silencing may occur due to an interaction between the two cortical pathways. Moreover, these results indicate that the illusion is established at an early age.

However, Peirce (2013) argued that silencing can be caused by any strong visual change. He conducted several experiments in which the dots from the illusion were modified in colour, size and aggrupation, with relatively slow motion. Results indicated that all these changes generated silencing, although the strength of the effect varied according to the modification applied. A possible explanation for silencing awareness of change could be that the crowding degree decreases change recognition.

Simons, Franconeri and Reimer (2000) suggested that silencing of awareness could happen in the absence of disruption such as motion or addition/deletion. To confirm this, the authors conducted an experiment where participants were presented with images that were disrupted – adding, deleting, changing colour- and they were asked to indicate whether they had noticed any variations. The results indicated that observers usually failed to notice the variation in the scenes. From this, it can be concluded that individual cannot encode every detail from the environment, therefore, visual changes which were not attended to, will not be perceived. This leads back to the hypothesis that attention is needed to process changes in our surroundings; nevertheless, the stimuli need to reach a certain threshold to attract attention.

However, they also observed that gradual changes were better perceived when the viewers saw the original and altered scene divided by a disruption. This advises that individuals seek and process gradual changes differently. For gradual changes without a disruption, subjects will not try to encode the scene as they are aware the change is happening. Contrary, when there is a disruption, subjects will try to encode visual details to detect changes. Thus, by attending they will locate modification easier.

Bach (2019) proposed that the illusion might be related to motion blindness (inability to perceive moving objects). Bonneh, Cooperman and Sagi (2001) research shows that motion-induced blindness has similar outcomes to the silencing effect. A possible explanation for silencing awareness of motion is that attention cannot be divided between two places, hence, why variation of the environment is not identified.

As it can be seen the silencing effect is not unique to the illusion as it can occur in circumstances where the illusion is not present, as indicated above. Regarding the mechanism of the illusion, it is still unclear seeing as there is limited research on it. Further research is needed to have a better comprehension of the mechanism. Moreover, attention should be taken into consideration as there is quite strong evidence that supports the hypothesis that it plays a role in detecting changes.