ATTENTION, CONSCIOUSNESS, SLEEP AND WAKEFULNESS 



1571 



et al. (72) have observed a similar thing in connection 

 with the auditory cortex of the cat where they find 

 that about 34 per cent of the units isolated by micro- 

 electrode methods could not be activated by sounds. 

 Galambos and collaborators (1 19) in studying single- 

 unit responses of the auditory cortex of unrestrained 

 and unanesthetized cats have also encountered units 

 which are unresponsive to sounds, unless the cat is 

 'paying attention' to the sounds. They have referred 

 to these as 'attention' units since they are so obviously 

 involved only in response to sound when the sound 

 commands the attention of the animal. They found 

 that about 10 per cent of the units examined were 

 units which responded only when attention was simul- 

 taneously manifest by the animal's behavior, such as 

 turning of the head toward the source of the sound, 

 and appearing to be alert and attentive. In Pavlovian 

 terminology this might be called an 'orienting re- 

 sponse' or orienting behavior. 



Such attention units characteristically would not 

 respond to clicks, tones or noises from a loud speaker 

 on repeated tests, although a new tone or noise might 

 evoke a response the first feu times it was presented. 

 A unit might respond briskly to the appearance of the 

 experimenter and to certain unique stimuli which at- 

 tracted the attention of the cat. For example, the 

 voice of the experimenter, squeaks of a toy mouse, 

 scratching sounds, hissing noises or tapping on a table 

 were effective in causing a unit, otherwise unrespon- 

 sive to repeated noises, to discharge. Clicks from a loud 

 speaker which were ineffective in Bring a unit would 

 do so the moment the experimenter pretended to tap 

 the loud speaker which produced the clicks and thus 

 drew the attention of the animal to the source of the 

 clicks. Hence it was evident that such units, presum- 

 ably 'adapted' or 'habituated' by repetition, could 

 regain functional status by some additional reinforce- 

 ment or 'disinhibition' brought about by an addition 

 or slight change in the stimulating situation. This 

 change would appear to be related to the ARAS or 

 DTPS rather than STPS. Galambos and lellow work- 

 ers conclude "that the neural processes responsible 

 for attention play an important role in determining 

 whether or not a given acoustic stimulus proves ade- 

 quate. Unfortunately attention is an elusive variable 

 that no one has yet been able to quantify. It may be 

 that studies in which cortical unit activity is examined 

 during the course of conditioning and learning will 

 illuminate these matters." 



Earlier Hernandez-Peon et al. (106) demonstrated 

 how 'attention,' in unanesthetized cats with elec- 

 trodes implanted in the cochlear nucleus, could in- 



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FIG. 8. Suppression of response in one modality by selective 

 attention in another Indwelling electrodes in the cochlear 

 nucleus of a cat for recording cochlear potentials to click 

 stimuli .1 cat relaxed, cochlear response strong. B: cat re- 

 sponsive and attentive to two white mice in jar, cochlear re- 

 sponse weak. (.': cat relaxed again, cochlear response to click 

 restored. [From Hernandez-Peon et al. 11 06).] 



fluence the response of the cochlear nucleus to clic ks. 

 Figure 8 shows a regular and uniform response from 

 the cochlear nucleus to clicks when the cat is resting 

 and not apparently attending specifically to the stim- 

 ulus (the obverse of certain cortical units mentioned 

 above which responded only when the cat was at- 

 tentive). When two mice in a glass jar are presented 

 and the cat's orientation and attention is obviously 

 focused upon them, the response of the cochlear nu- 

 cleus to clicks is greatl) suppressed. Olfactory and 

 nociceptive stimuli had similar inhibitory effects upon 

 the auditory response. Finally, when the mice or other 

 distracting stimuli are removed and the cat returns to 

 a resting state, the response of the cochlear nucleus 

 returns to its original magnitude. Here is an apparent 

 example of sensory inhibition imposed upon the sen- 

 sory pathways of a given modality when another com- 

 peting modality becomes the object of attention. Such 

 an inhibitory mechanism imposed at various synaptic 

 sites in thesensorv pathways suggests that the selective 

 exclusion of certain incoming signals mayoccur periph- 

 erally as well as at the cortex or thalamic levels. How- 

 ever, like the centrifugal negative feed-back system 

 mentioned earlier, of which this inhibitory attention 

 mechanism may be a part, the origin of the effect may 

 reside in the cortex or reticular formation of the lower 

 brain stem. The important point would seem to be 



