Cognitive neuroscience of visual object recognition
Agnosia is a rare occurrence and can be the result of a stroke, dementia, head injury, brain infection, or hereditary.
Apperceptive agnosia is a deficit in object perception creating an inability to understand the significance of objects.
Similarly, associative visual agnosia is the inability to understand the significance of objects; however, this time the deficit is in semantic memory. Both of these agnosias can affect the pathway to object recognition, like Marr's Theory of Vision. More specifically unlike apperceptive agnosia, associative agnosic patients are more successful at drawing, copying, and matching tasks; however, these patients demonstrate that they can perceive but not recognize.
Integrative agnosia(a subtype of associative agnosia) is the inability to integrate separate parts to form a whole image. With these types of agnosias there is damage to the ventral (what) stream of the visual processing pathway.
Object orientation agnosia is the inability to extract the orientation of an object despite adequate object recognition. With this type of agnosia there is damage to the dorsal (where) stream of the visual processing pathway.
This can affect object recognition in terms of familiarity and even more so in unfamiliar objects and viewpoints.
A difficulty in recognizing faces can be explained by prosopagnosia. Someone with prosopagnosia cannot identify the face but is still able to perceive age, gender, and emotional expression. The brain region that specifies in facial recognition is the fusiform face area. Prosopagnosia can also be divided into apperceptive and associative subtypes. Recognition of individual chairs, cars, animals can also be impaired; therefore, these object share similar perceptual features with the face that are recognized in the fusiform face area.
Effects of cannabis
When THC enters the blood stream and reaches the brain, it binds to cannabinoid receptors. The endogenous ligand of these receptors is anandamide, the effects of which THC emulates. This agonism of the cannabinoid receptors results in changes in the levels of various neurotransmitters, especially dopamine and norepinephrine; neurotransmitters which are closely associated with the acute effects of cannabis ingestion, such as euphoria and anxiety.
Some effects may include a general alteration of conscious perception, euphoria, feelings of well-being, relaxation or stress reduction, increased appreciation of the arts, including humor and music (especially discerning its various components/instruments), joviality, metacognition and introspection, enhanced recollection (episodic memory), increased sensuality, increased awareness of sensation, increased libido, and creativity. Abstract or philosophical thinking, disruption of linear memory and paranoia or anxiety are also typical. Anxiety is the most commonly reported side effect of smoking marijuana. Between 20 and 30 percent of recreational users experience intense anxiety and/or panic attacks after smoking cannabis, however, some report anxiety only after not smoking cannabis for a prolonged period of time. Inexperience and use in an unfamiliar environment are major contributing factors to this anxiety. Cannabidiol (CBD), another cannabinoid found in cannabis in varying amounts, has been shown to ameliorate the adverse effects of THC, including anxiety, that some consumers experience.