Optical Illusions

Figure 1. Gestalt Switch - Can you see the Eskimo?

Optical illusions are a great initiation point for people to start to explore Pivotal Mental States. Optical illusions provide the observer a quirk of perception which may seem strange at first however, they can often be explained from a evolutionary psychology perspective.

Gestalt Switch

In psychology, a Gestalt Switch is when a person's perception suddenly changes from one visual interpretation to another. For instance, the initial interpretation of Figure 1 is usually a face, however, given time, people can also see an eskimo. The reason the majority of people initially see a face first is that this is a prioritised type of human perception. It has been found that there are inbuilt mechanisms in the brain which canalize ambiguous information into the face processing part of the brain. Another demonstration of this is the Coffer Ambiguous Figure which takes advantage of the brain prioritisation of horizontal lines over rounded lines.

Magic Trick

Gestalt Switches can be framed or primed so that the presenter can force others to seeing one version of the image opposed to another. For instance, if you take Figure 1 and present it to someone else with the framing: "here is a a picture of an eskimo entering a cave" you will be able to force their perception into primarily seeing the eskimo.

Grid Illusion or Scintillating Grid

Figure 2. Grid illusion - where is the black dot?

The scintillating grid is a simultaneous lightness contrast illusion (Figure 2).

Effect

Dots which are not centred in your visual field should appear to flash from black to white, in a 'scintillating' effect.

Mechanism

It is thought the reason for the illusion is physiological. The mechanism proposed by Baumgartner (1960) detailed that the effect might be due to inhibitory processes in the retinal ganglion cells, the neurons that transmit signals from the eye to the brain. To each cell there corresponds a small region of the retina called the receptive field, where photoreceptive rods and cones can trigger an electrical response in that cell. The receptive fields of adjacent ganglion cells may overlap.

Troxler Effect

Figure 3. Troxler effect - looking at this long enough causes it to disappear.

Firmly fixating one's focus on a stationary object in the visual field can cause the surrounding visuals to appear to fade or slowly vanish (Figure 3).

Effect

Keep very still and keep your gaze focused on the central area of the image. Do not strain your eyes, but try not to let your gaze wander from the centre.

Mechanism

The Troxler effect illustrates the importance of saccades, the involuntary movements of the eye which occur even while one’s gaze is apparently settled.