1604 



HANDHIKIK OF rlt\slc .Y 



NEl'ROI'HYSIOI.OCV III 



mediate size among three objects differing in size; 



having learned to do so, the subject can, under some 

 conditions, 'transpose' this middle-size reaction to a 

 new set of objects of greater or lesser absolute size 

 (162, 407). Apparently, most discriminations involve 

 responses to relationships between the dbcriminanda. 



Similarity 



Closely related is the central problem of similarity 

 in perception. As Mach (333) pointed out, geometric 

 similarity is not necessarily identical with optic (or, 

 more generally, perceived I similarity, since we can- 

 not predict, on the basis of purely physical characteris- 

 tics of a stimulus, which patterns will be perceived 

 as similar. 7 Stimuli are similar in some respects 

 and not in others so that the problems oi similar- 

 it\ involve all those listed up to now, patterning, 

 selection and transposition. Perception of similarity 

 is basic to our capacity- for recognition, and thus for 

 inclusion of what we see or hear or feel into classes 

 oi stimuli. What the neural basis of such classificatory 

 activity might be has not even been a matter of 

 much speculation [but see Semon (419), Craik (94), 

 I hi ib (188) and MacKay (335)]. Some guesses 

 about it would be needed in understanding agnosia, 

 a condition claimed to consist of a specific loss or 

 impairment of this classificatory activity in the 

 presence of particular brain lesions. As we shall see, 

 however, there is considerable controversy as to 

 whether agnosia, in this sense of the term, could ever 

 occur. 



Serial I / emporal) Order 



A yie.it deal ol work on perceptual phenomena has 

 been restricted to the studv of --t.it it" patterns, usually 

 visual displays in two dimensions. While these pat- 

 terns serve to underscore the importance oi grouping 

 and perceptual selectivity, undue reliance on these 

 static demonstrations leads to a neglect of temporal 

 sequences in perception, the problems ol serial order. 



■ 1 . 1 k« the riddle "I octave similarity, To must listeners, 

 tones one 01 tave apart are more similai than are tones within 

 the octave, and tones differing l>\ an octave are readily con- 

 fused Perhaps Newton's preoccupation with the musical 

 u.is noi so strange afta all, although ii remains odd 

 thai he ga 1 octavi itructure to the visible spectrum ["he 



anthropomorphii charactei ol ilus attribution is lerscored 



by the difficulty ol showing octave similarity in animals below 

 < 1 although then ar< data suggesting that octave similarity 



iSlsIs I., I I .lis |it 



In most languages, the sequence of words in a phrase 

 conveys specific meaning, and the sequence of pho- 

 nemes within a word has crucial importance in all 

 forms of human speech (see Chapter LXYI11 1>\ 

 Zangwill in this volume). The apprehension of such 

 patterns of successive stimulations clearly requires 

 some temporary storage of the information received 

 at any one moment (62, 64), and capacity to deal with 

 the completed sequence as if it were a simultaneous 

 pattern. 



Equivalence of Certain Temporal and Spatial Pattt 1 n 1 



Lashley (307) has pointed out that within limits 

 we can apprehend a visual (or tactile) configuration, 

 irrespective of whether we explore it by scanning, part 

 for part, or whether we see it "at one glance' (or have 

 it impressed upon the skin). The neural basis for this 

 transposition of serial into simultaneous patterns is 

 unknown but would seem to require some central 

 mapping of temporal into (simultaneous) spatial 

 orders. 



If we look back upon this list of problems, it will be 

 apparent that they are interdependent. Nor is it 

 likely that the listing is exhaustive (5, 21, 489, 490). 

 Yet enumeration of these half dozen aspects of per- 

 ception should remind us of the existence of problems 

 which traditional physiology has rarclv considered. 

 The list may also help us to indicate a striking simi- 

 larity (in logical structure) between two seemingly. 

 unrelated fields; experimental embryology and the 

 psychophysiolosy of form perception. In both areas, 

 the origin of form is a central problem. In both, clues 

 for analysis can be derived from essentially three 

 sources: studies involving delect, isolation, or recom- 

 bination (530). In defect experiments, the develop- 

 ment of organic form (or perception of patterns) is 

 investigated in the presence of a lesion in the struc- 

 ture. In isolation experiments, the behavior of a part 

 of the structure is studied alter it has been cut off 

 from tin' remainder of the living svstem. or the entire 

 svstem is studied under conditions of artificially 

 diminished input. In recombination studies, finally, 

 one inquires into effects ol altered arrangement in the 

 spatial relationships ol parts, as in embryologic ex- 

 periments involving transplantation I ( ; ;, Vi" 1 . or in 

 studies of vision after inversion of eves in tlv or fish 

 or new 1 1 [48, 1 ;6, 1 (9), or alter the prolonged wear- 

 ing of distorting or inverting spectacles in man (285, 

 455 \'<~ ■ I It-Id, unpublished observations). We shall 



therefore turn next to a review ol normal pattern 



perception, especially the problems ol shape, selec- 



