In the Symbolic Cuing Task, upon given a cue that does require interpretation (endogenous), such as an arrow or the word "LEFT," subjects will likely voluntarily reorient themselves towards that event. There is a conscious steering of one's attention towards this cue, one that we need to interpret first. 

Posner: Endogenous Cue

In the Peripheral Spatial Cuing Task, upon given a cue that does not require interpretation (exogenous), such as a flash or spot in a certain direction, subjects will likely involuntarily reorient themselves towards that sudden event. Their reflexive attention has been reoriented towards this cue. This is considered to be a bottom-up process because attention is being captured and controlled by sensory inputs from lower levels of the nervous system.

Posner: Exogenous Cue

In most trials of the Posner Cuing Task, the cue given will be an arrow. A Valid cue would be where the arrow points in the correct direction, towards the target. Sometimes, however, there will be an invalid cue, where the arrow points in the opposite direction of where the target subsequently appears. With most subjects, there is a longer reaction time associated with the invalid cues as opposed to valid cues. 

Posner: Valid or Invalid Cue

The cue that appears before the target can be classified in multiple ways.
- Valid or Invalid Cue
- Exogenous Cue
- Endogenous Cue

New York University

Also known as the symbolic cuing task, in this participants stare at a fixation point in the center of a computer screen and must press a key as soon as they see a specific target stimulus; the response being measured is reaction time. Each trial is preceded by a cue that gives the participant a hint as to where the stimulus will appear.

Posner Cuing Task

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

During the cuing task, if the interval between the cue and target becomes too long (~200 ms onward), a noticeable phenomenon that has been noticed is that the detection of the stimuli at the location where the cue occurred is increasingly impaired. It's as though attention has moved on from the flash and is reluctant to return to that location. This inhibition of return is thought to prevent reflexively controlled attention from settling on unimportant stimuli for more than an instant. 

Posner: Inhibition of Return

On valid trials, electrodes measuring the activity of the occipital cortex show substantial enhancement of the event-related-potential component called P1, a positive wave that occurs over auditory cortex about 70-100 ms after stimulus onset. At longer intervals between the cue and target, the visual P1 effect may actually be reduced as an electrophysiological manifestation of inhibition of return. For invalid trials, where attention is directed elsewhere, the visual P1  effect isn't evident at all. 

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