Cell responses to static heads/bodies

Cells with viewer-centred properties

47/53 (89%) of all the cells selectively responsive to the static head/body were found to show viewer-centred properties in their coding of the whole body stimulus. That is, neuronal responses to one view of the body (the best/optimal view) was significantly different (greater) than responses to other non-optimal (worst) views of the body. As should be evident from most the figures used in this thesis, different cells were found to be tuned to different views (some responded maximally to the front view of the body, others to the back, others to the left profile, and others to the right profile etc.). Below I will describe the findings, using the classification of cell types established in chapter V.

Cells coding only one static bodv part

29/53 cells were selectively responsive to only one (effective) component part. These cells responded to the other component part at rates not significantly different to S/A or control objects (23 head alone and 6 body alone cells were tested). 97% (28/29) of the cells studied displayed sensitivity to view. These cells responded significantly different to a minimum of two views of the whole body. Furthermore, the majority of these cells (90%, 26/29) with viewer-centred properties for the whole body also showed view-selectivity for the effective component part tested with the same views as the whole body stimuli (see e.g. Fig. 6.1). The remaining 3/29 cells (2 body alone and one head alone cell) discriminated between different views when the whole body was tested, but did not discriminate between views for the effective body part tested in isolation (see e.g. Fig. 6.2). Since one cell discriminated between different views of the head presented in isolation, this phenomena cannot be argued to be due to little

responses (+/- ISE) of one cell (E99_40.16L) tested to view 0° and view 180° of the whole body and its components. Two-way ANOVA revealed a significant main effect of view [F(l,24)=31.3 p<0.0005]; body part tested [ANOVA: F(2,24)=9.3 p=0.001]; and interaction between these factors [F(2,24)=5.2 p<0.05]. Protected least significant difference tests (PLSD), post-hoc tests, indicated significant response discrimination between the different views of the entire body (p<0.0005) and of the effective body part tested in isolation, head only (p<0.0005).

Head alone cell; View discrimination □ Front View I

0 Back View ! 50 45 40 I 35 z>_{30 -} ^ 25

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Figure 6.2. Neuronal responses of a ‘body alone’ cell with viewer-centred properties to the whole body but not to the body alone. Histogram of response (spikes/sec) to different stimuli. Upper; photographic representation of stimuli used for testing. Lower; mean responses (+/- ISE) of one cell (E92_38.20L) tested to view 180° and view 0° degrees of the whole body and its components. Two-way ANOVA revealed a significant main effect of view [F(l,22)=4.5 p<0.05]; body part tested [ANOVA; F(2,22)=8.06 p<0.005]; however, there was no interaction between these factors [F(2,22)=0.12 p>0.5]. Protected least significant difference tests (PLSD), post-hoc tests, indicated significant response discrimination between the different views of the entire body (p<0.05) but not for the different views tested of the effective body part (body alone) (p=0.5).

70 -I

Body alone cell: View discrimination

fill If

□ Best View ; ■ W orst View

difference in the visual appearance of the stimuli tested when presented in different views.

Coding the entire bodv

Cells responsive to multiple static body parts

11/53 cells which were selectively responsive to the whole body and multiple component parts tested were tested for their sensitivity to different views of the whole body and the same views of the component parts. 7/11 cells were found to be coding the whole body and its component parts in a viewer-centred manner (see e.g. Fig. 6.3).

The view discrimination for the whole and parts was found to be compatible for all cells. That is, no cells responsive to multiple static body parts were found to only carry out view discrimination for the whole body but not its component parts. If a cell exhibited view discrimination between two views of an isolated body part, then the cell also showed the same direction of view discrimination for the whole body. Furtheimore, view sensitivity was observed to be similar for both component parts.

Cells only responsive to the static whole body

13 of all the cells (13/53) tested were selectively responsive to the whole body only and did not respond to the component parts of the body at rates significantly different than to S/A and control objects. The majority of these cells (12/13, 92%) were found to be coding information about the whole body in a viewer-centred manner (see e.g. Fig. 6.4).

Cells with object-centred properties

11% (6/53) of all cells tested for their selectivity to different views of the head/body showed no preferred view for either the whole body or its components (see e.g. Fig. 6.5). It should be noted that some of these cells were classified as object- centred on the based of only two test views (best and worst view).

One cell (1/29) of all cells selectively responsive to only one component part of the body was found to be coding information about the whole body and the effective body part in an object-centred manner.

Figure 6.3. Neuronal responses of a cell with viewer-centred properties to the body and its components. Histogram of response (spikes/sec) to different stimuli. Upper: photographic representation of stimuli used for testing. Lower: mean responses (+/- ISE) of one cell (B06_17.88R) tested to view 270 degrees and view 90 degrees of the whole body and its components. Two-way ANOVA revealed a significant main effect of view [F(l,27)=l 1.4 p<0.005]; but not for the body part tested [F(2,27)=0.3 p>0.5j; nor was there an interaction between these factors (F(2,27)=0.7 p>0.5]. Protected least significant difference tests (PLSD), post-hoc tests, indicated significant response discrimination between the different views of the entire body (p<0.005) and of the body parts tested in isolation, head only (p<0.05) and body only (p<0.()5).

Multi-part cell; View discrimination □ View 270

Ü View 90 45 1 40 - 35 - 30 - Q. 25 • w 2 0 - Control S/A Body Head Whole

(+/- ISE) of one cell (E08_26.50R) tested to view 0 degrees and view 180 degrees of the whole body and its components. Two-way ANOVA revealed a significant main effect of view [F( 1,16)= 10.46 p=0.0005]; body part tested [F(2,16)=7.3 p=0.006)]; and interaction between these factors [F(2,16)=11.2 p=0.001)J. Protected least significant difference tests (PLSD), post-hoc tests, indicated significant response discrimination between the different views of the entire body (the only effective stimuli, p<0.0005).

Whole Body only cell; View discrimination □ Front view Ü Back view ! 14 - o Q) </) W Q) 75._to 0) in cz o Q. to <u 0

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Figure 6.5. Neuronal responses of a cell with object-centred properties to tbe body and its components. Upper: photographic representation of stimuli used for testing. Lower: mean responses (+/- ISE) of one cell (E79_35.14L) to the back (view 180) and front (view 0) views of the whole body and its components are shown. 2-way ANOVA showed no significant main effect of the body part tested [F(2,24)=1.9 p=0.2] and no effect of view [F( 1,24)= 1.4 p>0.5] and no interaction between view and part tested [F(2,24)=0.2 p>0.5]. All responses to the whole body and parts stimuli in either the front view or the back view were significantly greater than control stimuli and S/A [ANOVA for the views: F(4,20)=6 p<0.005; ANOVA for the back views: F(4,20)=4.1 p<0.05).

Multi-part cell; Object centred □ Back view ■ Front view

w 30 Q. 25

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Whole

4/11 of the cells responsive to multiple static body parts showed object-centred properties when tested with different views of the stimuli (Fig. 6.5). All the cells coded information about effective body parts in the same object-centred manner as they coded information about the whole body.

One cell out of 13 static whole body only ceils did not discriminate between different views of the entire body tested. This cell responded equally well to the entire body presented in different views, but did not respond any differently to different views of the component parts than to S/A and control objects.