<p><strong>Short answer</strong><br>
Perception and imagination in the visual system use pretty much the same neural machinery, but in opposite directions - perception goes bottom-up, from the periphery to the central nervous system, while imagery uses the top-down approach, travelling from the higher associative cortices to the lower visual areas in the brain.   </p>

<p><strong>Background</strong><br>
The distinction between perception and imagination has received a lot of attention in the visual sciences. For example, imagery in congenitally blind individuals versus late-blind individuals is an interesting distinction to make with far-reaching consequences in certain fields of research (<em>e.g.</em> <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3111253/" rel="nofollow noreferrer">(Kupers <em>et al</em>., 2001)</a></p>

<p>Perception in the visual system goes from the periphery (retina), via the brainstem (LGN) to the striate cortex (V1) and higher extrastriate areas (V2-V7, see Fig. 1). </p>

<p>Content-related activation during imagery in visual extrastriate cortex is thought to be governed by “top-down” mechanisms in parietal and frontal cortex that mediate the retrieval of object representations from long-term memory <a href="https://linkinghub.elsevier.com/retrieve/pii/S0896-6273(00)00168-9" rel="nofollow noreferrer">(Ishai <em>et al</em>., 2000)</a>. Visual imagery and visual perception draw on most of the same neural machinery. However, albeit the vast majority of activated areas are activated during both conditions, the spatial overlap is neither complete nor uniform. The overlap was much more pronounced in frontal and parietal regions (higher visual areas) than in temporal and occipital regions (lower visual areas) <a href="http://www.sciencedirect.com/science/article/pii/S0926641004000709" rel="nofollow noreferrer">(Ganis <em>et al</em>., 2004)</a>.</p>

<p>I can't supply you with references on your following questions, but I wouldn't see any reason why the brain couldn't... </p>

<blockquote>
  <p>[...switch between] perception and imagination states, or [carry imagination and perception] out simultaneously</p>
</blockquote>

<p>Basically, perception and imagination are two separate processes sharing large parts of their pathways, but not being identical.</p>

<blockquote>
  <p>When an area sends information to another one, how does it signal whether this was perceived or imagined information?</p>
</blockquote>

<p>This distinction is quite clear and pronounced, as perception is bottom-up (retinae to extristriate areas), whereas imagery is top-down (extrastriate areas to striate areas in the cortex). </p>

<blockquote>
  <p>Is there less of a distinction between the two than I'm thinking?</p>
</blockquote>

<p>Indeed they are pretty similar as discussed and referenced above.</p>

<p><a href="https://i.sstatic.net/JATbj.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/JATbj.jpg" alt="visual system"></a><br>
<sup>Fig. 1. Visual system. source: <a href="https://au.pinterest.com/pin/527765650055756445/?lp=true" rel="nofollow noreferrer">Shumpei Ogawa</a></sup></p>

<p><sub><strong>References</strong><br>
<strong>-</strong> <a href="http://www.sciencedirect.com/science/article/pii/S0926641004000709" rel="nofollow noreferrer">Ganis <em>et al</em>., <em>Cognitive Brain Res</em> (2004); <strong>20</strong>(2): 226-41</a><br>
<strong>-</strong> <a href="https://linkinghub.elsevier.com/retrieve/pii/S0896-6273(00)00168-9" rel="nofollow noreferrer">Ishai <em>et al</em>., <em>Neuron</em> (2000); <strong>28</strong>: 979–90</a><br>
<strong>-</strong> <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3111253/" rel="nofollow noreferrer">Kupers <em>et al</em>., <em>Front Psychol</em> (2011); <strong>2</strong>: 19</a></sub> </p>

CC BY-SA 3.0
2017-08-14T22:37:08.273Z
Thank you! One question to your answer to my second question. I'd consider top-down modulation as part of perception. In that case, it's not obvious anymore how the distinction between top-down modulation of perception and top-down imagination is implemented. Those seem to be two rather different processes that at least in part use the same pathways. Am I missing something?
danijar
CC BY-SA 3.0
2017-08-15T09:41:34.290Z
@danijar the pathways are similar, but they go in opposite directions. Associations are made at the end of the perception pathway, whereas they are the starting point in imagery.
AliceD
CC BY-SA 3.0
2017-08-15T17:56:21.720Z
I understand that, but top-down signals also seem to be used to modulate the upward perception pathway. So then there are two different top-down signals: Modulation and imagination. Do you know anything about the distinction between the two?
danijar
CC BY-SA 3.0
2017-08-15T18:19:47.700Z
Can't help you out much further here; top-down processes on perception is basically where my knowledge ends. I've studied both processes, but not how they interact.
AliceD
CC BY-SA 4.0
2017-08-14T20:17:22.780Z
2018-07-06T06:35:58.110Z
2018-07-06T06:35:58.110Z
AliceD
<p>From my understanding, the neocortex performs both perception and imagination/planning within the same hierarchical structure. During perception, an area of the neocortex receives current input from sensors and decides on motor actions to execute. During imagination, an area replays previous inputs, or operates on potential future inputs for planning. Actions don't actually get executed during planning.</p>

<p>On the one hand, it seems like both perception and planning are in part executed by the same neural structures. It seems intuitive that the same abstraction mechanism needs to be reused to arrive at the same high-level representations. On the other hand, it seems like the brain still needs to distinguish between them, for example to not executed imagined actions.</p>

<p>The two processes certainly affect each other. Perceiving a difficult situation can cause planning, perception can cause an association to imagine another situation, or imagination sets filters on what we perceive. Are there any explanations if and how the neocortex implements both perception and imagination/planning within the same structures?</p>

<ul>
<li>Are perception and imagination states that the neocortex areas switch between, or can they be carried out simultaneously? Can multiple areas be involved in planning at the same time? </li>
<li>When an area sends information to another one, how does it signal whether this was perceived or imagined information? </li>
<li>Is there less of a distinction between the two than I'm thinking?</li>
</ul>

<perception><cognitive-neuroscience><cognitive-modeling>
How does the neocortex distinguish between perception and imagination?
danijar
# How does the neocortex distinguish between perception and imagination?

(Asked by: username_0 on 2017-06-09)

From my understanding, the neocortex performs both perception and imagination/planning within the same hierarchical structure. During perception, an area of the neocortex receives current input from sensors and decides on motor actions to execute. During imagination, an area replays previous inputs, or operates on potential future inputs for planning. Actions don't actually get executed during planning.

On the one hand, it seems like both perception and planning are in part executed by the same neural structures. It seems intuitive that the same abstraction mechanism needs to be reused to arrive at the same high-level representations. On the other hand, it seems like the brain still needs to distinguish between them, for example to not executed imagined actions.

The two processes certainly affect each other. Perceiving a difficult situation can cause planning, perception can cause an association to imagine another situation, or imagination sets filters on what we perceive. Are there any explanations if and how the neocortex implements both perception and imagination/planning within the same structures?

* Are perception and imagination states that the neocortex areas switch between, or can they be carried out simultaneously? Can multiple areas be involved in planning at the same time?
* When an area sends information to another one, how does it signal whether this was perceived or imagined information?
* Is there less of a distinction between the two than I'm thinking?

**Tags:** perception, cognitive-neuroscience, cognitive-modeling


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## 1 answers

### Answer by username_1 on 2017-08-14. Score: 6

**Short answer**  
Perception and imagination in the visual system use pretty much the same neural machinery, but in opposite directions - perception goes bottom-up, from the periphery to the central nervous system, while imagery uses the top-down approach, travelling from the higher associative cortices to the lower visual areas in the brain.

**Background**  
The distinction between perception and imagination has received a lot of attention in the visual sciences. For example, imagery in congenitally blind individuals versus late-blind individuals is an interesting distinction to make with far-reaching consequences in certain fields of research (*e.g.* [(Kupers *et al*., 2001)](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3111253/)

Perception in the visual system goes from the periphery (retina), via the brainstem (LGN) to the striate cortex (V1) and higher extrastriate areas (V2-V7, see Fig. 1).

Content-related activation during imagery in visual extrastriate cortex is thought to be governed by “top-down” mechanisms in parietal and frontal cortex that mediate the retrieval of object representations from long-term memory [(Ishai *et al*., 2000)](https://linkinghub.elsevier.com/retrieve/pii/S0896-6273(00)00168-9). Visual imagery and visual perception draw on most of the same neural machinery. However, albeit the vast majority of activated areas are activated during both conditions, the spatial overlap is neither complete nor uniform. The overlap was much more pronounced in frontal and parietal regions (higher visual areas) than in temporal and occipital regions (lower visual areas) [(Ganis *et al*., 2004)](http://www.sciencedirect.com/science/article/pii/S0926641004000709).

I can't supply you with references on your following questions, but I wouldn't see any reason why the brain couldn't...

> [...switch between] perception and imagination states, or [carry imagination and perception] out simultaneously

Basically, perception and imagination are two separate processes sharing large parts of their pathways, but not being identical.

> When an area sends information to another one, how does it signal whether this was perceived or imagined information?

This distinction is quite clear and pronounced, as perception is bottom-up (retinae to extristriate areas), whereas imagery is top-down (extrastriate areas to striate areas in the cortex).

> Is there less of a distinction between the two than I'm thinking?

Indeed they are pretty similar as discussed and referenced above.

[![visual system](https://i.sstatic.net/JATbj.jpg)](https://i.sstatic.net/JATbj.jpg)  
Fig. 1. Visual system. source: [Shumpei Ogawa](https://au.pinterest.com/pin/527765650055756445/?lp=true)

**References**  
**-** [Ganis *et al*., *Cognitive Brain Res* (2004); **20**(2): 226-41](http://www.sciencedirect.com/science/article/pii/S0926641004000709)  
**-** [Ishai *et al*., *Neuron* (2000); **28**: 979–90](https://linkinghub.elsevier.com/retrieve/pii/S0896-6273(00)00168-9)  
**-** [Kupers *et al*., *Front Psychol* (2011); **2**: 19](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3111253/)

> **Comments:**
> **username_0**: Thank you! One question to your answer to my second question. I'd consider top-down modulation as part of perception. In that case, it's not obvious anymore how the distinction between top-down modulation of perception and top-down imagination is implemented. Those seem to be two rather different processes that at least in part use the same pathways. Am I missing something?  
> **username_1**: @username_0 the pathways are similar, but they go in opposite directions. Associations are made at the end of the perception pathway, whereas they are the starting point in imagery.  
> **username_0**: I understand that, but top-down signals also seem to be used to modulate the upward perception pathway. So then there are two different top-down signals: Modulation and imagination. Do you know anything about the distinction between the two?  
> **username_1**: Can't help you out much further here; top-down processes on perception is basically where my knowledge ends. I've studied both processes, but not how they interact.  

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