Question

How long does an Iconic Sensory memory last?

Answer 1

Sensory (Iconic) memory is an ultra-short-term memory and decays or degrades very quickly, typically in the region of 200 - 500 milliseconds (1/5 - 1/2 second) after the perception of an item.

Explanation:

Iconic memory involves the memory of visual stimuli. It is how the brain remembers an image you have seen in the world around you. Iconic memory is part of the visual memory system which also includes long-term memory and visual short-term memory.

It is a type of sensory memory that lasts very briefly before quickly fading. Iconic memory is thought to last mere milliseconds before disappearing.
https://www.verywell.com/what-is-iconic-memory-2795272

Sensory memory is the shortest-term element of memory. It is the ability to retain impressions of sensory information after the original stimuli have ended. It acts as a kind of buffer for stimuli received through the five senses of sight, hearing, smell, taste and touch, which are retained accurately, but very briefly.

Sensory memory is an ultra-short-term memory and decays or degrades very quickly, typically in the region of 200 - 500 milliseconds (1/5 - 1/2 second) after the perception of an item, and certainly less than a second (although echoic memory is now thought to last a little longer, up to perhaps three or four seconds). Indeed, it lasts for such a short time that it is often considered part of the process of perception, but it nevertheless represents an essential step for storing information in short-term memory.
http://www.human-memory.net/types_sensory.html