<P> Semantic memory is also discussed in reference to modality . Different components represent information from different sensorimotor channels . Modality specific impairments are divided into separate subsystems on the basis of input modality . Examples of different input modalities include visual, auditory and tactile input . Modality specific impairments are also divided into subsystems based on the type of information . Visual vs. verbal and perceptual vs. functional information are examples of information types . Modality specificity can account for category specific impairments in semantic memory disorders . Damage to visual semantics primarily impairs knowledge of living things, and damage to functional semantics primarily impairs knowledge of nonliving things . </P> <P> Semantic memory disorders fall into two groups . Semantic refractory access disorders are contrasted with semantic storage disorders according to four factors . Temporal factors, response consistency, frequency and semantic relatedness are the four factors used to differentiate between semantic refractory access and semantic storage disorders . A key feature of semantic refractory access disorders is temporal distortions . Decreases in response time to certain stimuli are noted when compared to natural response times . Response consistency is the next factor . In access disorders you see inconsistencies in comprehending and responding to stimuli that have been presented many times . Temporal factors impact response consistency . In storage disorders, you do not see an inconsistent response to specific items like you do in refractory access disorders . Stimulus frequency determines performance at all stages of cognition . Extreme word frequency effects are common in semantic storage disorders while in semantic refractory access disorders word frequency effects are minimal . The comparison of' close' and' distant' groups tests semantic relatedness .' Close' groupings have words that are related because they are drawn from the same category . For example, a listing of clothing types would be a' close' grouping .' Distant' groupings contain words with broad categorical differences . Non-related words would fall into this group . Comparing close and distant groups shows that in access disorders semantic relatedness had a negative effect . This is not observed in semantic storage disorders . Category specific and modality specific impairments are important components in access and storage disorders of semantic memory . </P> <P> Semantic memory has had a comeback in interest in the past 15 years, due in part to the development of functional neuroimaging methods such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), which have been used to address some of the central questions about our understanding of semantic memory . </P> <P> Positron emission tomography (PET) and functional magnetic resonance (fMRI) allow cognitive neuroscientists to explore different hypotheses concerning the neural network organization of semantic memory . By using these neuroimaging techniques researchers can observe the brain activity of participants while they perform cognitive tasks . These tasks can include, but are not limited to, naming objects, deciding if two stimuli belong in the same object category, or matching pictures to their written or spoken names . </P>

Who devised the episodic and semantic model of memory and why