Key words: spatial ability, congenitally blind, cognitive structure and blindness, echoic memory, enriched environment.

Abstract
The congenitally blind have clearly a poorer spatial ability but a better musical ability and short-term memory than sighted and partially sighted. 3 out of 27 congenitally blind had and adequate spatial ability. Factor analysis showed that "The Owaki- Koh Intelligence Test for the Blind", mobility, practical skills and understanding of the physical world can be considered as one factor. Cognitive structures are influenced more by "when blind" than by "how long blind". Degree of light perception, overprotection
and physical surroundings influence cognition. The partially sighted and adventitiously blind have a cognitive structure similar to
a sighted person.
The sample consisted of 27 congenitally blind, 3 who became blind 2-3 years old, 6 blind at 5-6 years and 72 who either became blind later or were partially sighted.
 
 

Research results from cross-cultural psychology ( Berry 1966, Dawson 1967) may also help us to understand which factors contribute to the development of spatial ability. Strict rearing/overprotective parents are negatively correlated with spatial ability according to the studies of Berry and Dawson just mentioned.

What is spatial ability? One may define it as:
Possession of a coherent internal representation of space in which all activities, events and objects
having a relation to the physical world can be mentally placed, manipulated and understood..

Such a representation is often of a visual nature in man but not necessarily so. In the shower with soap in our eyes we find the towel with closed eyes because we have a representation of our surroundings which isn’t necessarily of a visual nature. We are living in the same physically world, blind or sighted, and through evolution man has developed a brain to cope with this world through various senses.

Linn & Petersen (1985) in a meta-analysis are discussing the concept spatial ability in relation to gender and types of spatial tests. On the basis of factor analysis of many different spatial tests and 30 studies, from 1974 to 1985, they ended up with three factors which they call spatial perception, mental rotation and spatial visualization. This is not "a final answer" but an attempt to classify certain spatial tests, and it shows that "spatial ability" is not a very unitary concept.

Why this focus on spatial ability? Because it is generally agreed that it is an important component of intellectual ability and especially mathematics (Geary, 1994) In relation to a blind person it is important because many practical skills seem dependent upon spatial ability.

Millar (1994, p. 1) asks how important vision is to the notion of space. "Is visual experience crucial?" What if "we do not take the role of vision for granted, and do consider movement, touch and sound as sources of spatial information?" "What information is missing and how can it be substituted" (ibid). Millar (1994, p.15) comes up with a model she calls CAPIN – Convergent Active Processing in Interrelated Networks. It implies that "the sense modalities are sources of specialized, but complementary and convergent information".(ibid)

Kitchin & al.(1997, p.369) asks; .., can a person with visual impairment or blindness achieve an adequate spatial representation of
a complex, real-world environment".

Rosenkranz et al. (1976, p. 188) write: "A frame of reference in ones internal representation of space seems to require a simultaneous global and symbol structure. If a person is born blind, such simultaneity can only be achieved through combinations
of perceptual symbol structures from different modalities. The congenitally blind may never develop the combinations to the point
of possessing a frame of reference."

Many factors may be of importance, e.g. what role does early vs. late vision play? Warren (1974) expresses that a blind person having had vision for some time retain a visual frame of reference or a spatial reference system. He goes on to discuss how
important the various stages of development are without drawing any clear conclusion due to lack of adequate research.

Stuart (1995, p.130) seems to have a different view. He is saying ".. the ideas of directionality in space are not represented in a modality-specific manner, but in a supramodal fashion in the parietal lobes bilaterally"

Schneekloth, L.H. (1989) argues that the physical environment is of great significance for the spatial development of the congenitally blind. Complex surrounding stimulate activity which again seem to be positively correlated with cognitive development. This is clearly demonstrated in an experiment with rats by Greenough et als. (1993) p. 301-302 in Johnson, M.H.(1993) They concluded that "merely making visual experience of a complex environment available to animals otherwise unable to interact with it has little behavioral effect." They reported that "several regions of the cerebral cortex were heavier and thicker in EC (Environmental Complexity) than in IC (Individual Cage) rats, and had larger neural cell bodies and more glial cells." Moreover ...the amount of surface available for synaptic connections, of up to 20%, were reported in the upper cortex of rats reared in EC versus IC environment, from weaning to late adolescence" (Greenough et als. (1993) p. 302 in Johnson, M.H)

Complex environment and activity seem both to be crucial factors for cognitive growth. Psychological- and anatomical results seem to support each other. The results are rather general. We don’t know with a great deal of precision what type of environment and what type of activity leads to what type of cognitive development. Moreover, optimal conditions may vary from person to person..

The effect of complex environment is discussed by Moser, M.B. (1999, p. 593) "Repeated exposure to such environment has been shown to increase the density of spines and dendritic complexity in relevant brain structure". The studies have been on animals like rats and mice, but may indicate that specific training can give development of certain brain structures and certain skills.

Maguire et als. (1997) report "the right hippocampus is recruited for navigation in large scale environments" They used PET method. An impairment or lack of stimulation of this part of the brain would also have negative effects on spatial ability. Some of the congenitally blind may have such neurological impairment (Potter, 1997, Stuart,1995) or have not got proper stimulation.

For the blind child is it also important that he/she can feel safe when moving around. (Schneekloth, 1989) Then the child dares to be more active and by that learn more.

"Little Room" (Nielsen, L. 1991) is built so the child shall get feedback and be stimulated to activity and thus evolve spatial concepts. An underlying idea seems to be that the blind child can generalize to the world at large. This seems in line with Crattys (1971) ideas for developing spatial concepts in congenitally blind children. Cratty emphasises development of a body image as crucial, as a base, for developing spatial concepts.

Similar arguments may be found among people working with sighted children. To have a situation which is limited in scope but with a clear structure may be an advantage in certain circumstances. Turkewitz & Kenny in M.H. Johnson (ed.) (1993), p. 516 write; "Sensory stimulation during infancy may not only promote subsequent perceptual organization, but it may also substitute for perceptual organization during early infancy by providing an orderly world for the infant." The authors are writing this in connection with how an infant explores mothers face about 20 cm away so that the infant is getting simultaneously tactile and visual input.

Neurological impairment may also play a negative role for developing the spatial ability, especially in congenitally blind. Both Potter (1995) and Stuart (1997) are discussing this.

The importance of activity for learning is also discussed in relation to malnutrition by Berry et als (1992, p. 375) where they point to that reduced activity due to undernourishment may be at least as damaging as direct negative effects on CNS.

From the studies reported above one may have learnt that; 1: Physical activity contributes to learning in general and development of spatial ability in particular. 2: Restricted but well-defined environment which allows feedback and activity contribute to the development of useful cognitive structures generally and spatial concepts in particular.

The present study may contribute to the understanding of point 1. It will further look at background factors, which may be of importance. Parent’s attitudes and physical surroundings will be considered among many other factors. Those factors have also been studied in cross-cultural psychology. If results from the two areas point in the same directions it may contribute to better theories with greater impact.

Congenitally blind children are especially vulnerable for inadequate or inappropriate stimulation from the environment. Consequently it can often be easier to demonstrate effects of various background factors in this group than in the population at large. Consequently, hypotheses developed in this area can be applied to the population at large.
 
 

The tests and questionnaires were partially standardized tests, partly constructed by the author.

The sample consisted of 27 congenitally blind individuals, 3 individuals who became blind between and 2 and 3 years old and 6 becoming blind 5-6 years old.. These two groups went through all the tests and questionnaires. 72 partially sighted and those becoming blind as grown-ups went through the three first tests described below.

The data was collected over a period of almost 4 years, from 1972 – 1976, when I worked in a school for the blind as a psychologist.
Description of the tests and questionnaires follows below.
 
 

2.1: Ohwaki-Koh Tactile Intelligence Test for the Blind.
The test requires that the subjects construct a pattern, presented on a piece of cardboard, with 4 (2x2), 9 (3x3) or 16 (4x4) cubes.
The cubes have 4 different fabrics. One surface can be fully covered with one type of fabric or two, with the border along the
diagonal, forming two triangles. All the cubes are identical. The test correspond to Block Design in WAIS.
This test is considered a test of spatial ability more than a test of "pure intelligence"
The partially sighted had a blindfold when tested.

2.2: WAIS, verbal part
This part of the test consists of the following six subtests: 1: Information. 2: Reasoning.
3: Arithmetic. 4: Similarities 5: Digit Span. 6: Verbal Comprehension.

2.3: Wings "Standardized Tests of Musical Intelligence"
The music comes from a piano and was presented by a taped recording. It consists of 7 subtests, but only the 3 first were used.
One reason was that their scoring is objective in the sense that the answers refer to physical properties of the stimuli. They are
called: 1: Chord Analysis (detecting the number of notes played in a single chord) 2: Pitch Change (Detecting an alteration of a
single note in a repeated chord). 3: Memory (detecting an alteration in a note in a short melody (3-10 notes) when played a second
time). The subjects shall say which note.
 

2.4: Memory for letters
The test were built up after model of "Digit Span" in WAIS.

2.5: Halsteads six forms
Task 1: Define or explain verbally the following forms: 1: Square. 2: Rectangle.
3: Semicircle. 4: Cross. 5: Parallelogram. 6: Eclipse

Task 2: Identify the same 6 forms engraved in a wooden plate.

Task 3: The subjects were asked to identify the same 6 forms as pieces of wood in three sizes:
a: The same size as in task 1. b: Half the size. c: Twice the size.

2.6: Natural forms:
The subjects were asked to give the form and size of the following 20 objects: 1: Door 2: Skating rink (oval/400 meter/one round) 3: 100 meters of straight road 4: Window 5: Soccer field 6: A block in a city. 7: Table 8: House 9: Box of matches 10:Bus 11: Road intersection 12: Painting 13: Flag on a pole 14: Book 15: Cigarette box. 16: Tree 17: Ship (medium size/passenger, boat/ferry) 18: River 19: Airplane. 20: Horse.
An assistant and myself made the scoring on a 0-3-point scale after having decided on the criteria beforehand. A "0" was no answer at all or an entirely meaningless answer, "3" meant an answer of the same quality as a sighted average person. Three students of special education were used as a reference point. The answers were scored both with respect to form and size.

2.7: Making a model of clay.
The subjects were given a piece of clay weighing 450 grams packed in a standard way. They were asked to make a man or woman ("menneske" in Norwegian). There was no set time limit. The scoring was on a 1-5 point scale along the following dimensions:
1: Details  2: Proportion 3: Total evaluation. 4: Similarity to a human.

2.8: Mobility
The mobility score consisted of the following elements: 1: Range. Score:1-5. 2: Can read a map. 3:Anxious to ask for help.
4: Getting to know a new place. 5. Using aids like the white cane, dog or a combination. Score: 1-3. Total evaluation of mobility:
Score 1-5.

2.9: ADL.
They were asked 10 questions with respect to practical skills. Each question was scored on a 0-3-point scale.
Max score: 30 points

2.10: Important background variables
a: Degree of light perception. Some people classified as totally blind turned out to have had or had some lightperception.
This point was investigated thoroughly both by interviewing, switching the light in the room on and off or turning on a light
in front of them. The following classification was made on this basis:
1 no light perception
2 can feel if the light is on or off under certain conditions
3 can see dimly the direction of light
4 can see forms dimly
5 can see outline of some forms

b: How much does light perception help?
1 no help, no light perception
2 keep direction
3 avoid objects in your pathway
4 keep direction and avoid objects in pathway
5 more help than 4 and 5

c: Surroundings. How favorable is the environment for moving around?
1= very little favorable environment, 5 very favorable environment. The subjects were questioned thoroughly about this point.

d: Parents' attitude with respect to what the child one was allowed to do.
1 very strict
2 rather strict
3 normal
4 rather liberal
5 very liberal

                                                    TABLE 1
                   Comparison of test scores of different groups of visually impaired.

Comments:
a: Spatial ability is on the average close to a 8 years old in the congenitally blind and strongly significant
from the partially sighted, but 3 out of the 27 congenitally blind had a spatial ability at the same level as
a sighted or partially sighted person.
b: Echoic memory is slightly better in the congenitally blind but not statistically significant
c: Musical ability is significantly better in the congenitally blind
 
 

                                            Tabel 2
PARENT ATTITUDE WITH RESPECT TO FREE MOVEMENT
Congenitally blind. N= 27

Degree Strict	N	Ohwaki-Koh	WAIS (verbal)
Poor	11	43	80
Medium	8	41	86
Good	8	67	110

 

                                        Tabel 3
ENVIRONMENTAL CONDITIONS FOR FREE MOVEMENT
                        Congenitally blind. N= 27

	N	Ohwaki-Koh	WAIS (verbal)
Poor	11	44	85
Medium	6	45	86
Good	10	66	101

 

                                                        TABLE 4
                                    VARIMAX FAKTORANALYSIS
                                    Congenitally and early blind. N = 36.

VARIABLES	Factor 1. Spatial	Factor 2. Music	Factor 5: G-factor	Factor 6: Echoic memory
Physical environment	,46	-,12	,18	-,11
Parents attitude: Strict-free	,42	,00	,51	-,14
Braille reading	,42	,37	,33	,35
Spatial ability: Owaki-Koh	,68	,13	,61	,06
Music 1: Cord analysis	,15	,81	-,07	,19
Music 2: Pitch change	-,10	,86	,05	,15
Music 3: Memory	,04	,60	,04	,56
WAIS 2: Reasoning	,34	-,01	,81	,29
WAIS 5: Digit span	,33	,25	,15	,85
WAIS 6: Vocabulary	,24	,07	,78	,34
Weeks too early born	-,37	,21	-,23	-,41
Size. 20 natural objects	,81	,08	38	,03
Form, 20 natural objects	,81	,05	,36	,17
Human of clay: Details	,46	,46	,53	,20
Human of clay: form	,59	,09	,62	-,03
Mobility: Distance from home	,78	-,32	,26	,18
Digit span: Forwards	,02	,12	,04	,87
Digit span: Backwards	,43	,27	,23	,71

Description with respect to size and forms of natural objects like soccerfield, bus etc. have a heavy
loading of factor 1 together with mobility and "The Owaki.Koh Test". Digit Span backward, but not
forwards has a considerable loading on factor 1. Digit Backwards correlates 0.54 with Owaki-Koh,
Digits Forward only 0.14.

                                                Table 5
Correlations with Ohwaki-Koh Congenitally- and early blind. N = 36

WAIS:			Natural forms
1: Information	,71		Size est. small	,61
2: Reasoning	,67		"""""" medium	,61
3: Arithmetic	,75		""""" large	,76
4: Similarities	,62
5: Digit span	,44		Model of clay
6: Vocabulary	,59		Details	,71
			Proportion	,85
Weeks too early born	-,36		Reading map	,74
			Mobility	,80
Halsteads forms			Letters forward	,34
Formdefinition	,72		Letters backward	,47
Formidentification	,69		Digits forward	,14
Size	,51		Digits backward	,54

Levels of significance: 5%: 0,32, 1%: 0,42, 0.1%: 0,52
 
 
 
 

    |                                                            Table 6
                Variables affecting the test results (independent variables)

Independent variable		N	Owaki-Koh IQ Mean	WAIS IQ verbal  Mean	Music test Mean	Natural Forms Mean	Man made of clay Mean	Mobility Mean	ADL      Mean
Age blind N=36	5-6 y.	6	90 **	114 *	49	51 *	3,83 *	4,33 **	3,83 *
	0-3 y.	30	52	94	51	40	2,50	2,60	2,83
Light per N=27	None	16	42 ***	83 *	54	35 **	1,94 **	1,88 **	2,06 **
	Some	11	68	106	47	48	3,36	3,36	3,82
Owaki-K N=27	< 31	7		68 ***	45	27**	1,29***	1,29***	1,29***
	>32	20		101	53	45	2,95	2,90	3,30
Parents attitude	Strict	19	46 *	84 **	53	38	2,21	2,05 *	2,26***
	Free	8	67	113	46	46	3,25	3,50	4,00
Physical surround	Bad	16	58 *	96	50	43	2,81	2,81	3,19
	Good	11	44	86	53	37	2,09	2,00	2,18

* = significant difference at 5% level, ** = 1% level, *** = 0.1% level
 
 

                                                   TABLE 7
                                               Echoic memory
Correlations between memory tests among congenitally and early blind. N=36
 

	Music 3 Memory	WAIS 5 Digit Span	Letter Forward	Letter Backward	Digit Forward	Digit Backward
Music 3	1.00
WAIS 5	.62 ***	1.00
Letter F	.39*	.70 ***	1.00
Letter B.	.54***	.75***	.47**	1.00
Digit F	.47 **	.81 ***	.68***	.45 **	1.00
Digit B.	.61***	.93***	.62***	.77 ***	.48 **	1.00

* = significant difference at 5% level, ** = 1% level, ** = 0.1% level
 

                                               TABLE 8
Characteristics of those three evaluated to have an adequate spatial ability. N=3

Subj	O-K	WAIS	Weight	L.P.	Use	D.F.	D.B.	N.F.	Clay	Mob.	ADL	Eat
1	81	86	2100	3	5	6	5	56	4	2	3	30
2	90	133	4000	4	4	8	7	48	5	4	4	28
3	91	131	2450	3	2	8	7	49	4	5	5	29

Explanations to the abbreviations: O-K= Owaki-Koh, WAIS= verbal IQ, L.P.=Degree of light perception of blind people on a 1-5 point scale, Use=how well is light perception utilized, D.F.= Digit Span Forward, D.B.= Digit Span Backward, N.F.= Natural Forms total score. Max= 60, Mob.= mobility evaluation on a 1-5 point scale, ADL= Activities of Daily Living on a 1-5 point scale where 5 is best, Eat= Eating and food making on a 1-5 point scale.
One of the three persons above worked as a carpenter and had vaguely seen light on light poles formed a row when he was a kid.
 
 

                                                    TABLE 9
                    Frequency table of 27 congenitally blind

IQ	Owaki-Koh Tac. IQ Test		WAIS-verbal part		Birth weight
	Frequency	Cumul. %	Frequency	Cumul. %	Grams	Frequency	Cumul. %
<31	7	26			<1000	1	4
31-49	6	48			1000-1499	6	26
50-59	4	63	1	4	1500-1999	2	33
60-69	5	82	4	19	2000-2499	3	44
70-79	2	89	7	44	2500-2999	0	44
80-89	1	93	3	56	3000-3499	7	70
90-99	2	100	2	67	3500-3999	7	96
100-109			2	70	>4000	1	100
110-119			3	82
120-129			1	85
130-139			4	100

 

The results here indicate that some congenitally blind can under favorable circumstances develop an adequate spatial ability. This may be considered the most important result of this study. One can never be sure of the experience of the blind compared with a sighted person but one can compare their performance both on relevant tests, verbal behavior in relation to the physical world and how well they can describe space with well-defined concepts of form and size. Out from this it is meaningful to talk about a spatial ability. The Owaki-Koh Intelligence Test for the Blind is labeled a non-verbal intelligence test, which can be compared with the subtest Block Design in WISC-R and WAIS, but it can also be considered a test of spatial ability. A similar test, Kohs Block Test, has been used in cross-cultural studies (Berry, 1966) and considered a spatial test. The fact that the test also correlates highly with mobility, practical skills and understanding of the physical world support this notion of spatial ability.

From table 9 it can be seen how spatial and verbal intelligence is distributed among the congenitally blind. 7 of the 27 who had 0 (zero) in raw score on Owaki-Koh were given an arbitrary IQ score of 31 corresponding to the norm of a 5-year old. Of those with with 0 raw score on Owaki-Koh one had a verbal IQ of 85. This indicates that there exists considerable verbalism in this group.

Another clear trend in the data is that the congenitally blind have a higher score on the music test compared with partially sighted. The reason for this may be that they attend more to auditory stimuli and some were trained musicians. They also score relatively high on auditory memory tests like Digit Span. They are clearly below on Owaki-Koh and other spatial indexes. By studying table 1 one may see how various factors influence the cognitive structure. On WAIS their lowest score is on Reasoning. This subtest is to a considerable degree a matter of reasoning about practical matters like "what would you do if you discovered a house on fire". It is very understandable that it is much harder for a congenitally blind to reason about such a matter.

Table 2 and 3 gives an indication of the effect of parent’s attitude and the environment, but due to the small sample it is difficult to get significant differences between groups. Therefore groups are divided in two as can be seen in table 6. Table 6 also shows how important light perception is in individuals classified as totally blind. A student of mine, (Holtet, A. 1976), concluded in his M.A. thesis, on the basis of samples from the present group, that it was more support for "the motor theory" than "the visual map theory" meaning that it seemed to be more that some light perception initiated behavior rather than it gave information of shape or form.

From table 6 it can be seen that those six getting blind between 5-6 years old have scores similar to partially sighted. They have also a normal birth weight, mean =3530 g. and

SD =73 g. compared with the group becoming blind between 2-3 years old which had a birth weight of 2645 g. and SD = 1004 g.

Light perception also plays an important role in relation to all dependent variables as can be seen from the results in table 6..

The Owaki-Koh test is a good predictor of ADL skills and mobility. It may be considered a good instrument for assessing how well a congenitally will cope with a lot of practical matters.

Parent’s attitudes had some effect while the physical surround did not bring about differences except for Owaki-Koh.

Musical ability comes out as one factor in most factor analysises in this material, and fits in with the literature which concludes that musical tests seldom correlate with other tests (Fjeldsenden, 1974). One partial exception in this study is subtest 3, Musical memory, which has equal factor loading on "music" and "echoic memory". When looking at table 7 it can be seen that memory for music, digits and letters have a lot in common, and this common factor may be called echoic memory and considered as one type of sensory register.

Table 5 shows that "Digits Backwards" correlates 0,54 with Owaki-Koh, indicating that it has a considerable spatial component. Other studies have showed that "Digit Backward" correlates highly with intelligence in groups with IQ below 100. Costa, L.D.(1975) , Griffin, P.T. & Heffernan, A. (1983) , Schofield, N.J. & Ashman, A.F. (1986). The results here fit well with the results reported in the literature referred to above.

How to develop an adequate spatial ability in a congenitally blind child?
Complex environment and activity in relation to this environment seem to be two crucial components for developing spatial ability to a satisfactory level, but maybe learning of some common structures like rectangle, circle, cross, the form of a room and a house may be of help because they are very common structures in a modern society. One could start with a small model and expand gradually to larger real life scales. The subjects in this study were encouraged to use the six Halsteads forms, described in 2.5 , when applicable to explaining and describe the 20 Natural Forms..

Conclusions:
The congenitally blind and those blind before three years old have a much poorer spatial ability than partially sighted and sighted individuals but are better at auditory tasks as musical tests and remembering digits. Adequate spatial ability can be developed in congenitally blind individuals but few do develop it. Two of those with a normal spatial ability had also a very high verbal IQ as can be seen in table 8. The third person, which could dimly see the direction of light and reported that light perception was of great help to him, had low average intelligence.

This study seems to go against Rosenkranz et al. (1976) view that "A frame of reference in ones internal representation of space seems to require a simultaneous global and symbol structure"

The congenitally blind may develop a frame of reference implying an adequate understanding and mastery of the physical world. High intelligence and stimulating environment conducive to interaction with the surroundings may facilitate development of spatial ability.

Processing of auditory information seems better in the congenitally blind than other groups. They do better in a musical test and auditory memory tasks. The reason for better performance probably is that they attend more to auditory input.
 
 

Bach-y-Rita, P. (1972) Brain Mechanism in Sensory Substitution. New York: Academic Press.

Bach-y-Rita, P. (1971) A Tactile Vision Substitution System Based on Sensory Plasticity. In Sterling et als. (eds.) 1971, 281-290.

Berry, J.W. (1966). Temne and Eskimo Skills. International Journal of Psychology, 3, 207-229.

BERRY, J.W. ET als (1992) CROSS-CULTURAL PSYCHOLOGY. Research and application. Cambridge University Press.

Casey, S.M. (1978) Cognitive Mapping by the Blind. Journal of Visual Impairment & Blindness, 72, 297-301.

Costa, L.D.(1975) The Relation of Visuospatial Dysfunction to Digit Span Performance in Patients with Cerebral Lesions. Cortex 11: 31-36.

Crattys, B.J. (1971) Movement and Spatial Awareness in Blind Children and Youth. Springfield, USA. C.C. Thomas.

Dawson, J.L.M. (1967). Cultural and Physiological Influences upon Spatial-Perceptual Processes in West-Africa. International Journal of Psychology, 2, 115-128.

Dodds, A.G., Howarth, C.I. & Carter, D.C. (1982) The Mental maps of the Blind. The Role of Privious Visual Exprience. Journal of Visual Impairment & Blindness, 76, 5-12.

Fjeldsenden, B. (1974) Translation of Visual Information Into Auditory Codes. Research Bulletin, 28, 19-56.

Fletcher, J.F. (1981) Spatial Representation in Blind Children. Effects of Individual Differences. Journal of Visual Impairment & Blindness, 75, 46-49.

Geary, D.C.(1994) Childrens Mathematical Development. American Psychological Association.

Griffin, P.T. & Heffernan, A. (1983) Digit Span, Forward and Backward: Separate and Unequal Components of the WAIS Digit Span. Perceptual and Motor Skills 56: 335-338

Johnson, M.H. (ed.,1993) Brain Development and Cognition. A reader. Oxford, UK. Blackwell.

Holtet, Arne (1976) Romoppfatning hos blinde og svaksynte . MA thesis. University of Oslo, Norway.

Juurma, J. (1973) Transposition in Mental Spatial Manipulation. American Foundation for the Blind Research Bulletin, 26, 87-134.

Kitchin, R.M. & Jacobson. (1997) Techniques to Collect and Analyze the Cognitive Map Knowledge of Persons with Visual Impairment or Blindness: Issuses of Validity. Journal of Visual Impairment & Blindness, 91, 360-376.

Linn, M.C. and Petersen, A.C. (1985) Emergence and characterization of sex differences in spatial ability: A meta analysis. Child Development, 56, 1479-1498.

Maguire, E.A., Frackowiak, R.S.J., & Frith, C.D. (1997) Recalling routes around London: Activation of the Right Hippocampus in Taxidrivers. The Journal of Neuroscience, 17 (8), 7103-7110.

McLinden, D.J. (1988) Spatial Task Performance: A Meta-Analysis. Journal of Visual Impairment & Blindness, 82, 231-236.

Miletic, G., Hughes, B, & Bach-y-Rita. (1988) Vibrotactile Stimulation: An Educational Program for Spatial Concept Development. Journal of Visual Impairment & Blindness, 82, 366-370.

Millar, S. (1994) Understanding and Representing Space: Theory and evidence from studies with blind and sighted children. New York. Oxford University Press.

Miller, L.R. (1977) Abilities Structure of Congenitally Blind Persons: A Factor Analysis. Journal of Visual Impairment & Blindness, 71, 145-153.

Moricca, L.S. & Slocum, R.V. (1977) Pattern Recognition on the Forehead: An Electronic Scan System. Journal of Visual Impairment & Blindness, 71, 164-167.

Moser, M.B. (1999) Making more synapses: a way to store information. CLMS Cellular and Molecular Life Sciences , 55, 593-600.

Nielsen, L. (1991) Spatial Relations in Congenitally Blind Infants: A study. Journal of Visual Impairment & Blindness, 85, 11-16.

Ohwaki-Koh., Y.: Manual of the Ohwaki-Kohs tactile block design intelligence test for the blind. The Ohwaki-Institute of Child Psychology, 15. Kita 5 bancho, Sendei, Japan.

Palazesi, M.A. (1986) The Need for Motor Development Programs for Visually Impaired Preschoolers. Journal of Visual Impairment & Blindness, 80, 573-576.

Potter, L.E. Small-scale versus Large-scale Spatial Reasoning: Educational Implications for Children Who Are Visually Impaired. Journal of Visual Impairment & Blindness, 89, 142-152.

Rock, S.L., Head,, D.N., Bradley, R.H., Whiteside, L., & Brisby, J. (1994) Use of the HOME Inventory with Families of Young Visually Impaired children. Journal of Visual Impairment & Blindness, 88, 140-151.

Rosencranz, D. & Suslick, R. (1976) Cognitive Models for Spatial Representations in Congenitally Blind, Adventiously Blind, and Sighted Subjects. The New Outlook for the Blind, 70, 188-194.

Schofield, N.J. & Ashman, A.F. (1986) The Relationship between Digit Span and Cognitive

Processing across Ability Groups. Intelligence 10: 59-73.

Schneekloth, L.H.(1989) Play Environment for Visually Impaired Children. Journal of Visual Impairment & Blindness, 83, 196-201.

Shayne, L.B. (1986) Age at Onset of Blindness and Development of Space Concepts: From Topological to Projektive Space. Journal of Visual Impairment & Blindness, 80, 577-582.

Simpkins, K.E. (1979) Development of the Concept of Space. Journal of Visual Impairment & Blindness, 73, 145-153.

Sterling, T. D., Bering, E. A. Jr., Pollack, S. V. & Vaughan, H. G. jr.: (Ed.) (1971). Visual Prosthesis. New York: Academic Press.

Strelow, E. R. (1976) The Development of a Spatial Sensing System for Blind Children. The New Outlook for the Blind, 70, 22-24.

Strelow, E. R. (1978) Binaural Sensory Aid: Case Studies of Its Use by Two Children. Journal of Visual Impairment & Blindness, 72, 1-9.

Stuart, I. (1995) Spatial Orientation and Congenital Blindness: A Neuropsychological Approach.

Journal of Visual Impairment & Blindness, 89, 129-141

Trøster, H. & Brambring, M. The Play Behavior and Play Materials of Blind and Sighted Infants and Preschoolers. Journal of Visual Impairment & Blindness, 88, 421-432.

Ungar, S., Blades, M., Spencer, C. & Morsley, K. (1994) Can Visually Impaired Children Use Tactile Maps to Estimate Directions? Journal of Visual Impairment & Blindness, 88, 221-233.

Vander Kolk, C. J. (1977) Intelligence testing for Visually Impaired Persons. Journal of Visual Impairment & Blindness, 71, 145-153.

Wallace, T. & Russel, W.M. (1979) Spatial Memory for Configuration by Congenitally Blind, Late Blind; and Sighed Adults. Journal of Visual Impairment and Blindness, 73, 13-19.

Warren, D.H., Anooshian, L.J. & Bollinger, J.G. (1974) Early vs. Late Vision: The Role of Early Vision in Spatial Reference Systems. AFB Research Bulletin, 26, 151-170.

Warren, D.H (1974) Early vs. Late Vision: The Role of Early Vision in Spatial Reference Systems. New Outlook for the Blind, 68, 157-162.

Warren, David H. (1976) Blindness and Early Development: What Is Known and What Needs to Be Studied. The New Outlook, 70, 5-16.

Warren, David H. (1976) Blindness and Early Development: Issues In Research Methodology. The New Outlook, 70, 53-60
 
 

http://www.sv.ntnu.no/psy/Bjarne.Fjeldsenden/BlindLinkM2000/Links2000.htm
This page has several good links related to blindness

http://www.sv.ntnu.no/psy/Bjarne.Fjeldsenden/LINKS499.htm
Look at "Blindness" at this link page